HOW: Start by lying on your back with your knees and feet in the air with a 90deg right angle at your hips and knees. In this position, engage your core and draw your ribcage down. Slowly bring your shoulders and upper back away from the floor. Your goal is to rotate and lift your left shoulder towards your right knee. Then lower yourself and repeat by lifting your right shoulder towards your left knee.
FEEL: You should feel your core and abs working to lift your shoulders off the ground, especially the sides of your core in your obliques.
COMPENSATION: Keep the movement slow and controlled.