The most basic stuff you want to do is to make sure sure you maximize your armys dmg output in combat. That is learn which units do bonus dmg against what and then assign targets accordingly in battle.
Eg: You want all your slingers to target his archers, this is harder than it sounds since he will have alot of them, they die fast and it is _not_ possible to shift click new targets like you can do in bw.
The game will look less messy if you play it more.