If someone more experienced could write a guide for Najd that would be great.
In my first game I had some early success but eventually I got beaten back to my starting position rather quickly.
Wouldn't say I'm super experienced with Najd but I found a relatively successful start (I'm using all dlc btw)
Take the mission to gain access to the sea, should always be there. Ally the Mamluks, they start friendly. Build 3 infantry and fast forward to dec 11, if haasa has more than 1 ally restart. In my game they allied Baluchistan, so I allied Hormuz (Baluchistan won't get access due to at war with neighboring ally). During the war build 2 more infantry to be able to siege the lvl 3 fort (it's more expensive to siege with 9 than 10 units because every attrition tick will halt the siege making it much longer)
Btw, if Haasa if allied to someone that can reach you and has a lvl 3 fort themselves as well, I'd also restart.
If you can, fully annex Haasa, if you can't due to an ally like Baluchistan in my case leave them 1 province, but make sure to take the fort and the 2 gems provinces. As soon as you can develop the gems provinces to 10 and give them to the burghers to offset increasing autonomy
Haasa has feudalism, take a loan and embrace it
Due to you getting 150 mil from your nobles you'll reach tech 4 before the AI, use it to beat up a small alliance of 2 people (like dawasir+someone or shammer+someone)
At this point you gotta go with the flow, I fought Shammar next (allied with Hisn Kayfa), then Dawasir+Oman. Oman typically only has 1 ally and he has a lot of cores on hormuz. I force converted and vassalized him (and annexed Dawasir) and got a defensive war with hormuz which I used to take all of Hormuz land except the island (had no ships)
At some point the Mamluks will call you into a war that they will win by themselves, run around, loot and help siege to farm favours. With the Mamluks Yemen and Ethiopia should be no problems
Hope that helps a little, the middle east is a lot like Europe now, alliances are really diverse so you can't plan out everything in advance like you could