Roll onto your left side and position yourself so that your knees are bent behind you, and you are resting on your left elbow and hip. Your body should be at a roughly 45* angle. Put your right hand on your hip, and raise your hip until your body is parallel with the ground, then lower.
Remember to keep your elbow and arm on the ground and your knees close together. This is a rocking movement, raising and lowering in an easy, steady rhythm. Keep your abdominal muscles taught, squeezing your obliques and pushing your left shoulder down toward your hip with each repetition.
Do 45 seconds of repetitions on your left side, then switch and do another 45 on your right.