1. Pick on the fat ones. It motivates everyone.
2. Teach them all to hit toward first base. Any mediocre guy can pull the ball, but to go the other way does more for their development as hitters. It also makes the games shorter, and every tee-ball game needs to be shorter.
3. I don't think stealing is allowed in tee-ball, so the 30 mins of sprinting CadensDad advocated for is absolutely nessecary.
4. Work on the fundamentals whenever possible. Slides to break up the double play should be done at every base, regardless of the situation. It will prepare the infielders to perform under pressure, and prepare the sliders for when they abandon baseball for soccer in high school.
5. Ice Cream.