HOW: Lay on your back with your knees bent and feet planted. Find your rectus abdominis muscle by palpating the bottom half of your belly. Inhale, activate the muscle, then exhale while you keep the muscle engaged. Relax completely at the end of your exhale and repeat.
FEEL: You should feel the oblique muscle activate and press into your fingers.
COMPENSATION: Avoid using your glutes and moving your hips/sit bones lifting off the floor. Avoid hiking the hip as you activate the oblique muscle. Keep your back flat.