Bend forward from the waist keeping your knees straight, thighs lifted and back flat (bend the knees and round forward to modify).
Just hang forward and relax your whole body. Be careful with your knees and squat down, relieving the pressure from your lower back.
Lift your hips up toward the ceiling and place the fingers under the heels so the little fingers touch, this allows the elbows to work around the back of the calves (as if you are touching your elbows behind you).
Touch your stomach to your thighs, your chests to your knees and after 2 to 3 counts press your face on your shins.
It is more important to keep your upper body pressed to your legs, the fingers under the heels and the elbows behind the legs than it is to straighten the legs.
Slowly lift your hips up to the ceiling as you press your face into your shins in a combined motion until you completely straighten your legs.
This is the forward bend done at the end of the Half Moon. Many beginners believe the forward bend is a part of the Half Moon. This is a combination of two postures; Half Moon with Hands to Feet pose (Ardha Chandrasana/Padahastasana).
Be conscious of the way you begin the posture. If your back is tight and stiff or especially injured, bend your knees as you lower your hands to the floor. You can even place your hands on your thighs to protect your back further. Take your time in the first set and soften, exhale, and relax as you shake out your hips and back. When it is time to grab your heels, try getting your hands all the way around the back of your heels which will help place the arms all the way around the back of your legs. Students with limited flexibility, do the best you can in keeping your hands and arms behind by bending your knees more. If you are not able to place your hands underneath the feet, grab a hold of your calves, or simple hold onto each elbow behind your knees. It is more important to touch your stomach, chest and face to your legs than it is to make your legs straight. Keep working to straighten the legs an inch at a time, using your arm strength to pull up on your heels. Be careful coming out of the pose, ascend the same way you went down, keep your knees bent and place your hands on your thighs, if needed.
Now that you are getting close to straightening your legs, press your face into your shins, as you lift your hips forward, toward the ceiling and front of the room. This combined movement will allow you to use your body for leverage in order to better stretch your hamstrings. An important concept in understanding the dynamics of yoga is isolation: flexibility and strength, relaxation and intensity, softening and hardening. Soften and relax the area you are trying to stretch, in this pose the hamstrings (back of the legs) and lower back, both connected by the sciatic nerve. Strengthen your arms pulling up on your heels and contract your quadriceps muscles. Don not allow the contraction of your arm strength radiate down into the lower back and back of the legs. When you are able to separate these two distinctive sensations your practice will noticeably improve.
As I travel the country doing workshops I often notice a big misunderstanding about the hand position in this pose. If your legs are straight and your upper body is flat against your legs, don not place your fingers under your heels. Instead, cup your heels from the side so the thumb, forefinger and the webbing between your thumb and forefinger touch the floor. If you place the fingers under the heels, it shortens the hamstrings and inhibits your flexibility. It is going to feel weird at first, but after a few times you should start experiencing a deeper stretch. One footnote: your hands will have a tendency to slide up, don’t let it happen, keep your hands down.
We are not done yet. Halfway into the pose slowly begin to look down at the top of your feet. Keep your chin on your shins, lift your shoulders up toward the ceiling, and pull your head to your feet. Don’t crunch your neck. Your neck vertebra should line up with your back vertebra. Toward the end of the posture; lift your hips up toward the ceiling and then scoop your tailbone under to stretch the muscles around the sit-bones. The final position is to touch your head to your feet.