Tank_Guy#3 said:
I attack, capture, enslave (rarely execute), and fight continue as fast as possible. The quicker I move, the more the enemy has to react (and more of them get to die).
You need to be proactive, not reactive. Let your enemy be reactive.
You need to adapt to your current situation and your enemy situation, if he has an huge army you will prob be reactive, if other way around you´ll be proactive, the important thing is to mesure what will you gain towords the number of men you´ll lose.
Inital game - Take or enslave
Mid/Final game - Enslave or exterminate
Specialize cities - ones are for taxes, others for infantry, others for missile units and others for cavalry. Therefore only autmomanage on empire size. Note Farms are essential after a harbor/market/road, in many cases its even best to make it before everything else.
Build order - harbors gives more money then roads or markets. Barracks and infantry on your bigger population city, cavalry on secundary city (less pop) and skirmishers/archers on frontier cities.
Specialize armies - make horse/mercenary armies to snipe out the weaker far away provinces and move a garrison behind to ocupy new cities. Meanwhile build the best troops and prepare to go for the goodie cities, use best troops against rebelions and everything on the way to target in order to enhance experience. Try to make an army that can be retrained on the enemy´s bigger cities, spy to see if they have the necessary buildings for that, otherwise build them yourself.
Never play bellow the maximum difficulty level, less is just a pure joke.
Always conquer Rhodes

, the extra money is just incredible.