I'm surprised no one has mentioned this but remember, surrounding an enemy with missile units is a great tactic. Of course if your arches are all in typical line formation facing the enemy they can brace for impact, but that's not what they're meant to do. Firing at them head long you're just gonna hit shield and that eats up arrows with little casualties, especially against elites.

It takes more effort than normal but try to run circles around your enemy. If they have cavalry you'd might as well forget this strategy but figuring if you're in the east, you're gonna be against the AS a LOT and they specialize in slow, tough as nails pike men, which any archer unit can run circles around. They'll start dropping like flies and to also give you a tip, hold your fire. Don't let them waste arrows shooting at shields.

Finally, when you're on a hill, spread your archers out. I had to figure this out the hard way, because they would fire up at the enemy, then land on the other side into my own men firing at their other side. .-.;

Be creative with the tactics though, and when you're just starting out, be conservative with your ammunition, you only have so much and you don't have it in your budget to be pumping out soldiers every turn from the casualties you shouldn't be getting.

However, once you get a few mining settlements you'll be good to go for the rest of the game.