Try some duchy for starters - Empires are rife with intrigue and everyone wants to kill everyone, and in case of muslims - it's mostly your family wants to kill each other. Simple tips that'll help to avoid a lot of crap:
1. NEVER upgrade anything that is not your demense.
2. ALWAYS upgrade income buildings first
3. Your culture retinue have full bonuses no matter what tech level you are. that means Heavy infantry cultural retinue will have +60% defence, for example.
4. If you want to storm astles easily - stick with archer retinue - archers have high Skirmish value and only skirmish is counted in castle assault. 6000 archer retinue can storm 2k garrison with ease.
5. proper eugenics is the key. Stay away from lisp, hapelip, hunchbacks, imbeciles and other people with such traits even if they are heirs to the empire - that trails will plague your dinasty for generations.
6. At first it may seem that stewardsip is the most important education, but in fact Diplomacy is the most powerful of all. it will help you to screw your dumb vassals that wiull pester you with their retared requests and demands with no cost. Otherwise, you'll have to bribe them - and only if have high intrigue.
7. RAPE AND PILLAGE!
8. Only Elective Monarchy allows you to choose heirs. I STRONGLY recommend you to change to EM, bcause otherwise you can end up with Inbred, hunchback, lisp, imbecile homosexual heir. And if you are Zoroastrian and screwing your sister daily, or a big fan of Game of Thrones, Inbred trait will plague you constantly.
9. Do NOT give your heir a fief to govern - once a ruler, he'll start to go hunting, have feasts and spawn bastards. It seems like AI tends to take most dumb choices and your Brave Gregarious Charitable heir can end up as Maimed Craven Gluttonous slob.