Small, but sometimes important, tactical tricks.

Sometimes I press the wait key, which they slyly hid from us. Sometimes (I still don't understand why) while playing against an opponent, you can open the console and see what they have built, bought, and for how much. Also, when the opponent approaches a place they shouldn't (for example, near archers), I lure them away from there (there are many ways to do this). All of this is simple, but it often helps me.