HOW: Get set-up standing near a wall, place one knee and thigh up against the wall with your thigh about parallel to the ground. Try to be standing tall or leaning slightly into the wall, then push your knee into the wall as hard as you can and also push with the leg that is in contact with the ground.
FEEL: You will feel your hip and butt muscles working on the leg that is in contact with the ground. You will also feel your hip and butt muscles on the side that is pushing against the ball against the wall.
COMPENSATION: Do not lose knee position on the wall, do not lean away from the wall or lean back, try to not let your knee excessively bend on the side that is in contact with the ground.