This simple Yoga Exercise prepares your body for the other Yoga Asanas. It strengthens the abdominal and lower back muscles and is often used to come up into the Head Stand. Performing the Double Leg Raise trims the waist and the thighs. If your muscles are weak, you may find yourself arching your lower back or using your shoulders to help lift your legs. To get the most benefit from this Yoga Posture, make sure that the full length of your back is resting on the floor and your shoulders and neck are relaxed.
STEP 1: Lie flat on the floor.
STEP 2: As you inhale, raise both legs, keeping your knees straight and your buttocks on the floor.
STEP 3: Exhale and lower your legs. Repeat ten times. Make sure that your lower back remains flat on the floor while you bring the legs down to avoid any spinal injury.
Be sure to keep your lower back and buttocks on the floor. Once you can perform the Double Leg Raise without strain, lower your legs as slowly as possible and keep your feet an inch or so off the floor between raises to make your muscles work harder.
I like your site but I must inform you that the British wheel of Yoga advises that double leg lifts are not safe because they can injure the back. Instead you should only do single legs or bend the knees whilst raising or lowering.