The first time you do this workout, do 3 sets of 12 to 15 reps on each leg. Next time, do 4 sets of 6 to 8 reps on each leg. Alternate your rep scheme each time you do the full routine.
How to do it: Grab one of the heavier dumbbells with your left hand and stand on your right leg. Keeping your spine naturally arched, hinge forward at the hips (pushing your hips toward the wall behind you), and allow the dumbbell to lower towards the floor. As you lower, bend your right knee slightly and lift your left leg behind you to counter your balance. Return to the starting position, keeping your back straight, extending right leg (make sure you're engaging your right glute muscle), and lowering your left leg (left foot should remain off the floor).