When I have more firepower: Position my infantry and archers on a hill, cavalry to the left. Charge with cavalry when enemy approach the line.
When I have less firepower: Position my army just behind a hill to block sight for enemy archers. Let them approach as to minimize their opportunities of shooting at my army. When the first enemy soldier is visible, charge with entire army to take the hill.
When my army is basically all men at arms / swadian knights: Follow me and position in a way that the opposing army is to my right, that way horse archers can't shoot at us. When there are no obstacles (trees, rocks) between our armies, charge.
If I'm a horse archer: Laissez faire for my infantry and archers, follow me for my cavalry and approach the opposing army to my left, so I can shoot at them. Order cavalry to charge when my infantry are about to make contact.