Here's a very basic warm up drill we did in college covering a lot of the fundamentals:
Feeding balls from the center, have the player:
1. Hit a groundstroke from the baseline while moving in (make sure its a smart, well placed shot, not aimless ball bashing)
2. Hit a first volley somewhere near the service line (make sure they are doing a split step and not just running through the shot)
3. Put away volley
4. Tap net cord and hit an overhead while backing up
Rotate out
Do this with all forehands, or one side if you have a lefty, then after a few cycles switch to the backhand side.