STANDING HEAD TO KNEE (DANDAYAMANA JANUSHIRSASANA) :

•Start with your feet together. Lift up your right foot interlacing your fingers a hair below the ball of the foot, thumbs behind the ball of the foot (if you are not able to hold your foot, modify by holding your right knee interlacing your fingers on the front of your knee with your right foot in dorsal flexion). 
•Keep your upper knee a few inches above waist level and gaze (drishti) about twelve feet out on the floor in front of you. Straighten, but do not lock your standing leg keeping the weight forward toward the big toe mound and tighten the standing leg thigh muscle to protect the knee.
•Think of lifting the thigh up into the hip and buttocks creating a foundation for the pose.
•Slowly extend your right foot out as far as you can while still maintaining balance. Students with tight hamstrings and lower backs; don’t kick as far in the first set so you can warm-up the sacrum, lumbar and back of the outstretched leg.
•Eventually extend all the way until the upper leg is parallel to the floor. Think of pulling the foot of the kicking leg in toward your upper body which will help to support your lower back instead of allowing the upper leg to pull you down to the floor, which could injure your lower back.
•Drop your shoulders.  Keep your wrists straight and relaxed and extend you arms, which will allow a greater range of motion in the kicking leg to stretch to your full potential. If your upper leg is bent, be patient and hold the posture as long as possible. Your heel should be farther in front than your toes to stretch the back of the legs (hamstrings).
•Once your upper leg is straight, tighten the quadriceps of the upper thigh, keeping a firm grip with your fingers, relax your wrists, elbows and shoulders. Then drop your elbows below the upper calf pressing the forearms into your leg.
•Round and curl your upper body, keeping your stomach off your thigh, bring the chin to the chest (Jalandhara Bandha), and lower your forehead to your knee. 
•In the final position, the elbows are below the calf and the kicking leg is parallel to the floor.

ULTRA-ADVANCED:  After obtaining the full position, lower your hands down to your heels, with your right hand let go of your foot and extend your right arm out toward the front wall parallel to your outstretched leg, fingers together, palm facing to the left. Then extend your left arm out toward the front wall, parallel to your outstretched leg, fingers together, palms facing each other. Look ma no hands! Your upper thigh will burn and cramp at first. Be patient!

JIMMY'S TIPS:

Beginners:

Make sure you pick a spot to set your focus, on the ground, approximately twelve feet in front of you. If you focus on one spot it will improve your balance. Make sure your upper knee is a few inches above your waist to avoid lower back injury!! If your upper leg is still bending, drop and relax your shoulders and completely extend your arms. This allows for a full range of motion stretching out your upper leg. Be patient, this is one of the more advanced postures in the sequence.

Intermediate:

Assuming your upper leg is locked, relax your wrists! (As I travel the country I notice many people have a “death grip”) Since the wrists and forearms are so tight, they have trouble releasing when it’s time to drop the elbows down. The wrists must drop like a hinge, as the shoulders and elbows drop simultaneously. Hold on with your fingers, not your palms so you can feel the grip, allowing the arms the freedom to drop and release.

Advanced:

Now that you are in the full head to knee position - Congratulations! Your “primary thought” for the rest of your yoga career: keep your upper thigh muscle tight and engaged!!  This will insure your balance as you drop your elbows and head. During the final position, ninety percent of students need to lower the elbows even more. The elbows should be below the calf muscle, and the spine needs to round like the rabbit pose. So, round your spine and drop those elbows!!