HOW: First get into the hollow position by drawing your ribcage down and towards your hips. Slowly lift your legs and upper back off the floor to form a shallow "C" position. This is your hallow position. Once here, rock back and forth while maintain your hallow position like a see-saw.
FEEL: You should feel all the muscles in your core working to not only maintain the position, but while you are moving as well.
COMPENSATION: Try not to bend at your shoulders and hips to create momentum. Once you are rocking back and forth, pretend you are a rigid C without any excessive movement of your hips or shoulders.