PROPER SQUATS : Bring your toes to the wall, almost touching, then sit down. Stay looking straight so you learn to keep your torso up. Sit as low as you can go then hold the seated position for seconds and repeat. Great for butt, legs, and core.
Tighten your core with this one exercise! I would rather have a strong core than tight and dysfunctional one. PUSH therapy is probably the only system that teaches how to "strengthen" your core without tension and dysfunction.