As I mentioned in the Open Leg Rocker post if you struggle with rolling back and up and maintaining the hold on your legs you can do the same exercise without holding onto your legs until you can. So, here's a prep I love to do. For several reasons. It helps you feel the muscles you need to hold the shape of the Open Leg Rocker and because it also preps you for the reach and length you'll need in the advanced Rocker with together. The key with preps is to use them and then try to do the exercise in its original form. If you still need the prep, no worries, but don't assume you do. Your body will be ready before you think.
Pull your shoulders on your back then reach your arms toward your toes.
Setting yourself up for your Open Leg Rocker either by bending your knees and grabbing your ankles and trying to straighten the legs or by lifting both legs up towards your hands. Try to do one or two Open Leg Rockers to see what is tight, loose or simply not connecting. Then, balancing at the top flex your feet and reach your hands for your toes. Rock back and balance at the top 3-5x. Trying to reach your fingers past your toes even while you are on your shoulder girdle hips up.
After a few reps re-grab your ankles and attempt the Open Leg Rocker exercise. Often times I have seen students be able to do it once they realize they can reach their arms forward even when they roll back. The common mistake in Open Leg Rocker is for practitioners to let their elbows bend and the weight of their legs collapse on or towards their torso. Then they have to swing the legs forward...good luck trying to control those legs when you do that. If you can keep your arms straight throughout the exercise you will eventually get it!