Beginner: Beginners must use caution when approaching this posture. Be very mindful of your back and only go as far as you feel comfortable and no further. It is more important to maintain your alignment than it is to get your toes to touch the floor. A prop placed beneath the spine or resting your feet on a chair or block may help you express the pose safely.
Advanced: The advanced practitioner knows how to safely approach this pose. Regardless, always take care on the first roll back, as flexiblity varies from one day to the next. Once you are in the pose, continue to lengthen through the spine and reach through the feet and toes. Can you lift through the spine while in the posture? Try to create an open feeling in your chest as your spine curls over it.