* The AI is attracted to your hero in tactical combat. Use your hero to
  lure enemy units into a killing zone of ranged fire. For nonhero fights,
  this trick works with a ranged unit out front. Retreat your siege engines
  from combat as soon as the wall is breached. They are too expensive to 
  be destroyed by token infantry attacks. 

* Migrate friendly citizens to every city you conquer unless you are in a
  big hurry or need gold immediately, in which case, you should just loot.
  Never raze, unless it is a victory condition.