The basic trick when trying to beat the enemy, is simply engaging them in the front with infantry, then charge them in the back with cavalry while they are fighting the infantry.

When you do that, you cause a LOT of casualties in a short time, and more importantly, you cause so much morale damage that unless they are super troops, you will start a chain rout - which is the way you win battles.

Oh, and also target the enemy general quickly, killing him makes it much more likely to break the enemy.