Alright, ever play any Medieval strategy games or maybe Rome: Total War? Imagine that, only small scale. If you have a mix of cavalry, footmen, and archers, first, go to a hill or something high and order your archers to hold position there. Then, tell your cavalry to follow you. Go around back and flank the enemy from behind with your cavalry while your infantry takes them from the front.
If you have infantry whilst they have cavalry, like we said, get on a hill and pray to God there are enough spearmen in your group.
If there aren't many hills, get right on the other bank of a river. The horsemen are dead men riding while they cross it, especially if you have archers.
Archers are the worst against cavalry, that's probably what you would want to take out first with your cavalry. They move so quickly that they probably won't get a shot on you, that's why they suck so badly against horsemen.
If they have a ton of infantry and you have a lot of cavalry, they probably win, UNLESS you have Vaegir horsemen. They aren't armored very well and if the infantry is thickly packed enough, your cavalry will die, probably one-by-one. I'm sorry, but I just think Vaegir sucks, overall. Really. If you have Swadian men-at-arms, however, they have good armor, and they'll take out the infantry just fine.