I alter my strategy depending on who and where I'm fighting. These are the general rules I stick to:
1. Archers on a hill near infantry. I usually have more infantry the archers, so the enemy attack the infantry, not archers.
2. Cavalry far away, me with them and them set to follow much more effective than just saying charge to get them right in the flank, or hit their archers.
3. in sieges, I like to have get my infantry just in front of the archers as a shield wall, and when the archers are done, order an infantry charge.
4. If using siege towers, I get my infantry to follow me and hold the tower, creating a Termopylae situation, usually with the side walls of the tower adding protection from archers.
5. When fighting the Khergits, I get my infantry on a hill and as their light cavalry try to go up it, I strike with my cavalry. Otherwise it takes forever chasing their horse archers and the casulties can get overwhelming.
Other than that, use common sense and try to adjust to the situation.