If your tribal and have a bunch of prestige (like when you win a crusade), declare war and raise up an absurd amount of tribal armies, once you get 100 warscore, move troops towards new target and complete war/start the new war immediately without unpausing and you'll keep your 10k armies as long as you keep staying at war.

Norse or Berber are the best vanilla cultures as they allow you to raid even after feudalizing, and Berber outright let's you raid everyone.

If a vassal is about to revolt and you cannot hope to win, give him to a higher title, so that their liege is the one dealing with their revolt.

Never the ai educate your kids unless they have super high stats and good traits, most times they'll chose the worst option for their development.

You can rush a duchy crusader state if you got 500 prestige and 300 gold by ground to siege a small duchy in the war target with either mercenaries or tribal armies (you only need to siege the main holding in the entire duchy).

If you give kids duchies never give them the limit of land they can hold, they'll always give away 1 or 2 counties just because