These workouts are good for improving your kicking that I have used in my workouts.
Perform 6 sets of 10 repetitions each.
Lunge:
Go down into a lunge and come back up.  Then perform a front kick with your front leg.
You can perform this exercise for the round kick and the side kick.
Squat:
Spread out your legs shoulder width apart and perform a squat repetition, then as you come up, perform a front kick. 
Challenge:
Perform a squat and then a jump front kick to add in a little plyometrics.