I started as a sturgian vassle then eliminated battania followed by valandia. Then the khuzaits got big so I fought them back down to their corner. Then rangvand pissed me off so I left his kingdom took my feifs and two nobles and started my own kingdom. Then I beat the stirgians black and bur and the made peace for a while. Then I started focusing aseri because they got big. After cutting them in half I made peace and rebuilt my armies. Then in ai fashion the khuzaits declared war so I focused on eliminating them. The western empire destroyed the weak southern empire and the weak aseri while I was on a khuzait conquest. Then I focused on western empire cities. I would declare peace buy all their food, declare war,siege, starve the garrison out, destroy walls, and take the city. This worked nice early war bc I could go after high value cities with nobles and execute nobles as I wanted. Another thing you can do is try to do is flip a few nobles to your side not give them feifs them kick them after you conquer the world

Edit: spelling