This exercise might look really easy, but let the picture fool you. If you are a beginner, it is best if you do this exercise with both legs on the Balance Ball.
Place your hands wide apart, this will help you balance your self. Your hips should be off the floor, make sure you keep your core tight. One of your legs will be on the Balance Ball the other up in the air, you can bend it, or keep it straight.
Roll the Balance Ball in a steady pace with your heel firmly pressed inn while squeezing your Glutes and the back of your leg.
Do 3 sets of 10 on each leg. It will be a bit challenging in the beginning. This exercise is one of the best to Isolate the Glutes.