So, you want to be awesome at Humans. That's great, but first you need to not suck at them, and that's what I'm here for. I'll give an overview of what the Humans are good at and what they suck at, including an analysis of all of the units on their roster, including temple units. You can work on putting Sun Tzu to shame once you have a better grasp of the fundamentals, which should only take me about 20 pages or so if you were to put 4000+ words into paperback format. Even if you don't really suck at Humans, there's enough stuff you might pick up something useful here.
Stuff Humans Do Well
Humans are good at producing gold. They get an extra +100% gold producing building that none of the other races get, the Treasure House. This is a big deal, partly because Human units tend to take more gold than other resources and partly because gold has no practical limit on how much you can put to use, unlike food or mana. More on that later.
Humans can't build temples to Grum-Gog, but they can build temples to any other god. Undead and Monsters are restricted to four temples each, so they have a hard time combining the benefits from multiple gods to get a mix of temple units. Humans also have upgrade paths to temple units from their mundane lower-tier units, which makes producing huge armies of temple units a much easier prospect for the Humans than the other races, even if you only have one temple.
Humans also get the Silverwork Armory buildable on Silver resources, which gives a big damage boost (+20% Spirit and +20% Life damage) to Fighter and Ranged type units. Almost nothing resists Spirit damage. Living units typically have 100 Life resistance (which means you're looking at about a 25% damage increase against almost all living units) but Undead usually have -25 Life resistance. Against Undead, Silver Weaponry increases your damage by nearly 50%, and it only costs 50 gold for the upgrade. Make getting a source of silver a priority.
Humans can also build a unique building on Magic Fields that gives +10 Food and +10 Mana income per turn, at a cost of -4 gold. If you can find one or two of these, you're set for food for quite a while. Building up to a Magic Bazaar in those towns for double mana income and casting mana boosting spells, especially Dark Ritual (Fervus spell) is a very good idea.
Stuff Humans Suck At
Humans are bad at winning fights with just the units on their normal roster. Many of their units are lackluster compared to their counterparts in other races, and none of their regular units stand out as being exceptionally powerful like Trolls or Vampires.
Humans also have something of a disadvantage in early game scouting, which isn't crippling but it's worth noting. Undead can get Bats fairly early and easily scout huge swaths of the map, especially island maps or maps with lots of lava or other bad terrain. Humans' best scout is the Hunter, who have Scout and Forester along with four movement. Monsters get Ratman Robbers, who also have Scout and move through forests without penalty, but have five movement and more hit points. The other races can build starting units in two turns, but Humans can only build Warriors initially and they take three turns each. Humans also have to build a special building (Rangers Guild) to train Hunters, and the Rangers Guild is a dead end on the building tree. Monsters and Undead train their scouts from buildings that start the gold-income building branch, and which generate a small amount of gold themselves.
Regular Unit Analysis: This is the Crap You Have to Work With
The regular roster of Human units is rather lackluster. They get a couple of good units (Cutthroats, Mages), a few mediocre ones (Veterans, Hunters, Magisters), and an easily-skipped line of crappy ones (Clerics, Healers). They don't get anything anywhere near as powerful and generally useful as Old Trolls, and the expensive stuff on your roster is still really squishy and easy to kill. You make do with these things until you can get temple units, which can instantly kick your whoopass engine into high gear.
Warriors: These are the only unit you can build at first. They take longer to build than other factions' tier 1 fighting units, but have better armor. They're slower than Goblin Spearmen and don't hit as hard, but they have a very slight advantage over them in combat, and have much better missile resistance. They're pretty good at taking early cities, but not as good at it as Skeleton Warriors. I don't like them much due to their slow speed and longer build time. Still, if you're facing Undead you'll need these guys.
Veterans: Upgraded Warriors with more hit points and armor than any other normal Human unit. In fact, Warriors and Veterans are the only normal units on the Human roster who even have armor at all. There are a few armored Temple units, but I'll cover those in a separate section. Their offense is on par with Skeleton Veterans and weaker than Seasoned Goblin Spearmen.
Hunters: These are your best scouts as a Human player. They can travel through forests without penalty and get a bonus when attacking or defending in forests. They have the Scout perk, granting them +1 sight radius. They have two main drawbacks: first, they take a special building to train that doesn't lead to any other buildings. Second, they are squishy as hell. No armor and 12 hit points means a lot of units or monsters can kill them in one hit.
Rangers: Upgraded Hunters. These guys are kind of disappointing. They have the same movement and scouting abilities as Hunters and have fully twice as many hit points, so they aren't as prone to getting killed in a single hit by weak monsters. Tougher stuff still drops them in a single hit, and they have fewer hit points than tier 2 archers for the other races. Their missile attack of 11 is one better than the archers of other races, and combined with Silver Weapons they can hit pretty hard. Just make sure you keep them protected.
Rogues: These are one of the rare human units that actually compares favorably to other races. Rogues have an attack strength of 8 Melee, 4 Death, meaning they hit harder than any other tier 1 unit. They also have 19 hit points, which isn't as good as any of the Warrior units or their equivalents but it's not too bad either. They have no armor and they're very fast, with 5 movement. They're cheap and you can train them in any city with a Rogues Guild; since the Rogues Guild starts the gold income branch of the building tree (which is a big deal for Human players) you should be able to build these units just about anywhere.
Cutthroats: Rogues were good, these are even better. Cutthroats have an attack strength of 11 Melee, 11 Death. They hit harder than any of the basic units, and only cost 80 gold and two turns to build. They are very fast and have 35 hit points, which is the same as Seasoned Goblin Spearmen. They still don't have any armor, but these are still excellent units; they have a slight advantage over Veterans or Seasoned Goblin Spearmen in a straight up fight, and if both sides have some basic armor upgrades they win by an even bigger margin due to Death damage resistances. Against Humans or Monsters, these should be your standard fighting unit. Don't use them against enemies that are immune to Death damage, though. Depending on your choice of temples, they can do other really cool stuff too, but I'll get to that later.
Clerics: When you think of Clerics, you probably think of a formally trained religious figure, possibly armored if you've played tabletop RPGs. When you think of Shamans, you probably think of somebody who lives in the woods and licks toads, or smokes something and then wanders around in the desert. One would assume that Clerics would have a better understanding of the healing arts since they can, you know, read, but this is wrong. They have an 8 point heal (Shamans heal for 10) they can cast every other turn, and can attack for 8 Spirit damage two hexes away (Shamans hit for 10), which almost nothing resists. They have no armor (Shamans have 25), but do have weak (25) elemental resistance, so I guess that's something. The building that trains them does not lead to any other structures, so I typically skip them entirely. A Cleric costs as much as two Cutthroats. You should build more Cutthroats instead.
Healers: Like Clerics, except better at fighting and three times as expensive. Healers have 37 hit points compared to the Clerics' 25, and attack for 14 Spirit, 7 Life. Against living targets they hit about twice as hard as Clerics, and against Undead they hit about three times as hard as Clerics. They can cast a healing spell for 14 hit points every other turn. All of this can be yours for just 25 easy payments of $19.95 (500 gold). This is not a good deal. For the same price, you can train five Rogues simultaneously at all of your gold-farming towns (you should have a lot of those; that's why you're playing Humans) and upgrade them all to Cutthroats. Or you could get most of a temple unit. Or you could get three Mages. Clerics should probably cost 100 gold instead of 160, and Healers would be a decent unit at half their current price. The only redeeming feature is that Vampires have -25 resistance against both Spirit and Life damage, meaning a Healer can kill a Ghost or a normal Vampire in a single attack, or drop an Elder Vampire down to half a dozen hit points. I'd maybe consider building these if the enemy has a ton of Elder Vampires or something.
Mages: These guys are interesting. They do 17 Elemental damage at range 2, and a lot of their level up perks increase their damage. They have a spell that does 25% more damage than their base attack in Elemental damage, has a range of 3, and a cooldown of three turns. It also reduces enemy movement by two points, and gives -20 to Melee and Elemental resistances. If you have several mages, lead off with the spell from one of them to increase the damage from the other mages and any melee attackers you have handy. They cost 175 gold, which isn't cheap, but it's worth getting a couple of them just for the firepower and spells.
Magisters: Cooler than Mages, but also about three times the price. They have 32 health instead of 22, and do 24 Elemental damage instead of 17. They also grant all adjacent units (including themselves) +50 resistance to missile attacks. Their spell does more damage since ther base damage is higher, but it has the same range, debuff, and cooldown. Two or three Magisters moving in close formation are basically immune to missile damage, and their good damage output makes them reasonably effective at killing anything that isn't highly resistant to Elemental damage. Still, they're expensive to build and cost a small fortune to upkeep (10 gold, 2 food, 6 mana) so I usually don't bother getting them. Stick with Mages instead; they provide the same long range damage/debuff functionality at a third the price. Late in the game when you're swimming in gold, you might as well upgrade them then.
Catapult: This is a unique Human unit with no direct counterparts among the other races. Catapults are extremely slow (2 movement) and do moderate damage (13 Missile) that gets a lot of improvements as they level up and is doubled against cities. They also attack from three squares away, making them the only non-temple unit that can do this, although Mages can cast their spell three squares away once every three turns. Catapults take their own special building to train, and you need to babysit them so they don't get killed, since they have low hit points (21) and no armor. On the positive side, random monsters don't typically respond to units three squares away, so you can hammer away at units like Greater Fire Elementals on holy sites with impunity. If you're playing on an aquatic map, you can occasionally get a catapult to fire across a narrow channel and hit an enemy city when they can't fight back. Once you get Water Walking, a Catapult attacking from water is very safe and extremely powerful. With a couple of levels or upgrades they sink Tier 1 ships in a single shot and Tier 2 ships in two. Transports are always a one shot kill. Haste and Levitation are also good options for buffing Catapults, to help them get around the map faster and keep them safe from melee attacks that could kill them in a hit or two.
Temple Unit Analysis: This is Why You Play Humans
Temple Units are really what the Humans are all about. They have several advantages in this regard: first, Humans can build temples to any god except Grum-Gog, who is a goblin-lover and probably retarded, so you're better off not hanging out with him anyway. Second, many of the temple units can be upgraded from inexpensive regular Human troops. The Monsters can upgrade Court Werewolves to various temple units as well, but Court Werewolves require extensive infrastructure to build and cost 600 gold to train, so upgrading them is prohibitively expensive and mostly a lateral move anyway. Humans can generate the gold necessary to get a lot of temple units and the easy upgrade paths mean you can crank out temple units from a lot of cities simultaneously by upgrading regular units. This is a big deal, and it's why I've abandoned my previous stance that Humans suck. So, on to the units themselves.
Priestesses of Agrela: These are the best healers in the game, hands down. They have the same offense as the upgraded Cleric unit (14 Spirit, 7 Life) but a more potent healing spell that restores 17.5 health at a range of two with a two turn cooldown. They have 40 hit points, which is tied for second-lowest among all temple units for all factions. What makes them interesting is that they have a second healing spell that restores 28 life to a unit and all adjacent units with a range of 4 on a three turn cooldown. You can alternate spells to have a heal ready almost every turn. You can probably upgrade to these from the Cleric/Healer line, but I haven't bothered to check since Healers cost 500 anyway and you don't really need a lot of these even if you do decide to build them.
Paladins of Dauros: These guys are undead-killing machines. Slow and heavily armored, they do a combination of Melee and Life damage with their attacks. Damage output against living enemies is fairly low, but nobody wrecks Undead like Paladins of Dauros. A big part of the reason why is the spell they can cast, which does 28.5 life damage at a range of 2 and hits all enemies adjacent to the target, on a two second cooldown. Undead are vulnerable to life damage, so you can reliably get about 40 damage out of it against Undead. That's enough damage to kill Elder Vampires, Dracoliches, and Flying Line Galleuses (Galii? How pseudo-Roman are we pretending to be, here?) almost every time. In fact, the only normal Undead units that will survive this on a regular basis are Veteran Skeletons and Zombies. Paladins of Dauros also can't have blessings/curses dispelled from them, which is kind of a liability since the AI doesn't dispel buffs anyway.
Archers of Helia: These archers have two things going for them: range and elemental immunity. They've got decent armor against melee and missile attacks as well, but they have fewer hit points than any other temple unit (36). They can attack normally at a range of 3 with a strength of 14 Missile, 3.5 Elemental, and have a spell that does 21 Elemental damage at a range of 4 on a three turn cooldown. They also have the Scout and Forester perks in common with Hunters and Rangers. You can upgrade Rangers to these guys if you want, which basically means you're going to pay 850 gold instead of 700 for the unit in exchange for training them anywhere that you can build Hunters. Humans are gold-making machines, so this is well worth it and you might save money on the deal if you're building them at a town next to expensive upgrades.
Blademasters: Krolm's temple unit, there's nothing complicated about these guys. They hit really hard (35 Melee) and have a lot of hit points (70) along with light armor and some Elemental resistance (35). You can upgrade Veterans to these guys, which is a good idea since Warrior>Veteran>Blademaster isn't very expensive and Blademasters are faster than Warriors and Veterans. Units that do a mix of damage types only get partial benefit from spells like Frost Weapon; it increases the damage of the largest type, so a unit that does 10 Melee damage goes to 10 Melee, 2 Elemental if you cast Frost Weapon on it. If you cast Frost Weapon on a unit with 5 Melee, 5 Death damage, it would only do 5 Melee, 5 Death, 1 Elemental damage. Bigger damage numbers from a single damage type mean more effective percentage based spells and upgrades, and the only units that do 35 base damage of a single type are Blademasters and Gold Dragons. They have an ability that lets them hit three adjacent units in an arc in front of them for 43.8 Melee damage as well, usable every other turn.
Sisters of Krypta: These units inspire a lot of comparisons to Elder Vampires. Both cost 700, do a ranged Death attack, and have 40% health stealing. Sisters of Krypta are better in that they do 24 Death damage compared to Elder Vampires' 21, cost 10 gold and 5 mana to upkeep (Elder Vampires cost 8 of everything), and don't explode when exposed to life-based damage like Undead usually do. They also have Death damage immunity and 50 Elemental resistance. Elder Vampires have better Elemental resistances and a useful damage/stun spell. Sisters of Krypta get a Summon Skeletons spell that's really only useful as a mediocre scout. The skeletons summoned have 7 attack, not many hit points, and disappear after three turns, whereupon you can summon more.
Beastmasters: Fervus' temple unit is another archer type, and in my opinion they're better than the Archers of Helia. They have a fairly powerful attack (20 Missile) at normal archer range. They have the Scout and Forester perks like other Human archers, but they have a move speed of five instead of four like Archers of Helia. They have 50 hit points vs 36 for the Archers of Helia, and regenerate 8 hit points per turn. They have no armor, but have 50 resistance against Elemental damage and Spirit Damage. Spirit damage resistance is nearly impossible to come by in this game (Druids, the Monsters' temple unit for Fervus, also have it) and they have a lot of it. Finally, Beastmasters have the ability to summon Old Wolves once every three turns, to serve as scouts or medium-strength combat units. Old Wolves have 15 Melee attack, 27 hit points, reduce adjacent enemy power by 19%, and have a movement speed of four. You can also upgrade your Rangers to Beastmasters any time you want.
Assassins: Lunord's temple unit is, in my opinion, the best temple unit available to any race or any god. They have a stronger attack than any other temple unit (19 Melee, 19 Death) and have respectable armor (50 Melee resistance, 110 Ranged resistance, 100 Life resistance, 15 Elemental resistance) and decent health (55) along with very high movement (5) and inherent Invisibility when not adjacent to an enemy unit. They also have an ability that does 42.8 Death damage and drops an enemy's resistance to Death damage by 50, which means it takes twice as much damage from Death sources for two turns. Finally, you can upgrade Cutthroats to Assassins, and since you should have Cutthroats all over the place anyway, you should have plenty of high-level candidates as soon as you get a temple to Lunord. They aren't very good against most Undead since half of their damage is Death type, but with upgrades even that doesn't matter. If you add Silver Weapons it adds 3.8 Spirit damage and 3.8 Life damage, which translates into a little over nine extra damage once you take Undead vulnerability to Life into account. Without any upgrades other than that one, you're looking at 28 damage to Undead, which is enough to drop a Vampire about half the time. Further upgrades and level perks will have you killing Elder Vampires in a single hit. Against powerful non-Undead like Old Trolls (90 hit points, regeneration 20) you can pair up two Assassins to use their special ability in sequence. The first one does 40+ damage, and the second one gets the benefit of reduced Death resistance to do 80+ damage. Nothing survives this. Heck, even a one on one fight against a Blademaster that leads off with the special ability will drop him to less than half health and drop about 1/3 of your own health in the first round, and the second round kills the Blademaster while dropping your own health to about half. To sum up, Assassins are fast, hard to kill, invisible, easily upgradeable from the cheapest unit on your roster, and kill just about anything in no time flat, including most melee-specialized temple units.
Religious Strategy: Two-Timing the Gods
Monsters and Undead have a pretty simple approach to religion. They pick a god who doesn't hate them and do whatever they can to improve favor with that god. The other gods that they are adjacent to the chosen deity might offer them a few spells, but probably won't offer them temple units with the exception of Agrela/Grum-Gog for Monsters and Krolm/Krypta for Undead. Those aren't anything special since Champions of Grum-Gog are sort of mediocre and Krolm's Housecarls are easily the worst temple unit in the game. Humans can play it that way and chase a single god, but they have the option to easily get buddy-buddy with two or even three gods if you play your cards right. My preferred strategy for two-timing the gods is to start with Favor of Fervus. Fervus gets awesome spells, including a +60% Elemental Resistance buff and a +15 Regeneration buff that are both researchable fairly early and make killing the Fire Elemental guardians of holy sites a cakewalk. Once I get a holy site, I build a Temple of Lunord to get Assassins and move me closer to Lunord. At this point, I'm about equidistant from both Fervus and Lunord on the relationship wheel, and if I keep alternating between building temples to each of them I'll gradually move to a spot between the two of them but quite close to both. Once you have a temple to Lunord you can upgrade your Cutthroats to Assassins, and a Temple of Fervus lets you upgrade Rangers to Beastmasters.
Let's suppose you want to get a little more complicated and take a three god approach, like Agrela/Dauros/Helia. To get a good mix of magic/melee/ranged temple units. Build your first temple to Dauros, your second temple to one of the gods on the side, and your third to whichever one is last. Basically you just need to keep in mind that if you piss off a god too badly they won't let you build temples to them, and making a beeline for Agrela will piss off Helia and screw up the plan. You'll want to alternate temples between the two gods on the side as you acquire new holy sites. Any increase in your standing toward Dauros beyond the inner circle of the relationship wheel will actually move you further away from the other two gods, so the sweet spot on the relationship wheel is the point directly in between Agrela and Helia, where the line toward Dauros intersects the inner circle. Humans have an easier time fiddling with divine relationships because many of their temple units are easy upgrades from cheaper units on their regular roster, so you never have to worry about stuff like "I want to get closer to Fervus, but I need more temples to Lunord so I can build more Assassins simultaneously." Upgrading regular roster units to temple units lets you burn through gold much faster than you can possibly make it if you want to, and it's money well spent instead of wacky nonsense like putting Adamantium Armor on Goblin Spearmen.
Well, that's pretty much it for Humans. As a special super-secret bonus for reading the end, I'm including my fool-proof guide to winning with Monsters: spam Old Trolls and throw them at enemy cities. One per city is probably enough. Seriously, they're broken.