I use formations to approach enemy formations. I go with the 3 line missle, melee, cavalry. I use this to give my archers a clear field of fire and keeps my melee units out of enemy range. Once I get to my preselected stopping point I bring my calvary units to the wings and begin to circle. If my opponent charges my archers have a nice wall of melee units to retreat behind.

Obviously this plan is very basic and changes with the make up of my forces. Hope it helps.