Increasing your leg strength will help you build stability in your stroke. It will also help improve body position. Remember to kick with your whole leg. You can generate significantly more power from your hips than you can from kicking from your knees.
Warmup
4x50's Freestyle @:20seconds rest
8x50's Kick with board (focus on straight legs, power from the hips) @:20seconds rest
Main
5x25 Freestyle @:10 seconds rest
4x50 25 Single arm Freestyle / 25 Full Stroke Freestyle @:20 seconds rest
3x100 Kick with a board @:30 seconds rest
2x150 Freestyle pull @:45 seconds rest
1x200 Full stroke Freestyle @1:00 seconds rest
Warmdown
200 easy choice