Lie flat on your back on a mat with your legs straight and your arms extended alongside your hips, palms flat on the mat.
Lift your legs about 6 inches off the ground.
Begin the movement by lifting one leg higher than the other. As you are lowering that leg to starting position (6 inches off the floor), raise the other. This should be a fluid fluttering (or up and down) motion. Your feet should never touch the floor. This keeps tension in your core.
Try to complete sets of 15 to 20 repetitions, or try for a set amount of time such as 30 seconds to a minute (as you build strength).
Complete 3 sets with one minute of rest between sets.