The Clamshell exercise works your gluteus maximus, gluteus medius, and gluteus minimus.

-Start on the right side of your body and once you come down to the mat, make sure your knees at a 45 degree angle, so you don't want them right up in front of you, but rather to 45 degree angle. Now, lay all the way down on right side, let your head rest down on your right shoulder. Left hand stays flat on the mat in front of you. Now, flex your feet, and lift your ankles up off of the floor. Now, open that left off, and lower it back down. Every time you open up the thigh, try to squeeze your cheeks. Now, you wanna take 10 of those, finish and hold at the top. Extend that top leg right at the knee and come back to your heels. Take 20 full extensions, keeping the knee totally still and after your 20th one come back to the heels and just press back with that top knee 10 times to finish and then release and make sure you go onto the other side, so that you can do your right leg.