If playing Genoa, do not take provence. or anything bordering France. France gets a mission to ruin your day almost immediately.
Trade is immensely op now. Here are some tips to maximize your free money.
First, do not keep a merchant in your home node, the bonus is negligeable.
Second, unless it is a neighboring node funneling into your home node, collect from trade do not steer. Aside from a few idea combinations, it is not worth making steering trains (caveat, I havent dealt with african trade, may be different there.)
Third, trade fleets of 10 are what I use to protect trade. Nothing that special about the number, just keeps things tidy. You will appreciate tidyness as you start dealing with 5+ nodes and 6 10 different fleets.
Fifth, you do not actually need that many provinces to dominate trade. Just take the ones with bonuses, and you will do fine. Keeps AE down and makes it easier to keep the big bads of europe happy with you.
Some more tips.
Expand very slowly as a Holy Roman Minor. Take advantage of force vassal feeding by ceding them provinces in war, and try to spread out of the HRE proper as quickly as possible. For example, taking bites out of burgundy, poland, and the teutonic order.
Idea groups are not just the ideas themselves. Each one also has several events that come with it, that give thier own bonuses. Some are extremely potent, like humanist with the bonus tax base events, and religion giving free stability and prestige.
Rule of thumb, Morale in the early game, Discipline in the late game. Of course, both is best.
Having trouble with the ottomans? alley austria and poland. In 1.8 both of these nations seem to be itching to kick some turkish butt, I have yet to have them not answer my call to war if they were not already busy.
All by yourself and the ottoderps are closing in? Blockading the sea of Mamara works again in 1.8. Spam those galleys danny boy, spam them hard. Fun fact, Galley spam also helps for the berber states when it is time to deal with the ibereans. All ships are built the same in EU4 (aside from tech upgrade) so you can chunk aragon early and win some trade wars.
Did you win the lottery and PU france as Mantua? Is sweden getting surly and moving for idependance? Then it is time to be a super warmongerer! either France will be stuck on your side in war until it accepts your rule, or you can lose and release the tigers tail.
Colonizing gives something to do while AE cools down. You don't have to mess with the new world, mess around with africa for a bit, then return to europe to expand your land power when people forget about you.