Here is what I like to do.
Note: on all of these, don't simply hit into the net - back up at least 20 or 30 feet from the net so you can see the trajectory of the ball.
Round 1: Normal up the middle off of tee.
Round 2: Load + hold drill. Sometimes I have trouble getting my front foot down in time. This drill is simply getting into my load position and taking my step, firmly planting on the ground, then waiting a second before completing the swing phase of my swing.
Round 3: Walk up drill. Stand approx. 5-10 feet behind the tee, then just initiate the forward movement towards the tee by stepping behind your front foot with your back foot, and then land your front foot down and swing with all the momentum. Builds some nice power and athletisism in swing.
Round 4: 3 tee drill. Set up 3 tees, all on the same plane, and all in the same horizontal plane. Put balls on all three of them, and try to hit all of the balls off the tee. The point is to have the bat head in the zone for as long as possible.
Round 5: Skater drill. This is sort of hard to explain. Hopefully this makes sense. Take 3 back and forth lateral-plyometric jumps, then land on the 4th on your back foot, then come down with your front foot, and swing off the tee.
Round 6: Normal tee - 3 balls in each of the 9 spots of the plate.
Round 7: Normal tee - up the middle.
Hope this helps.