HOW: Get set-up laying flat on your back with your legs straight. On the side you plan to perform the exercise, bend your knee to a position that feels comfortable and that you can dig your heel into the ground without it moving, a 90 degree angle is a good place to start. While keeping your knee still, dig your heel into the ground as hard as you can trying to bend your knee, but nothing should be moving. You can change the knee angle based on what you need to work on.
FEEL: You should feel the muscles behind your thigh and your butt muscles working.
COMPENSATION: Do not arch your back, do not bend your knee, do not lift your butt up off the ground.