HOW: Start by assuming a plank position on a swissball with your toes on the ground and your elbows on the swissball. Actively push into the swissball through your elbows with your shoulder blades. Your shoulders should be active. Once in a stable and comfortable plank position on the swissball, slowly begin to rotate the swissball in circles. You will want to "stir the pot" with your elbows.
FEEL: You should feel all the muscles in your core and shoulder blades working to maintain the position.
COMPENSATION: Do not let your back overly arch or your hips to shoot up into the sky. Keep your shoulder blades engaged and do not let your shoulder blades come together.