Ardha Baddha Padmottanasana

In a standing position bring the lateral portion of your right foot onto the anterior portion of your left thigh.  Bring your right foot as anterior as possible by rotating your rectus femoris externally  Innervate your gluteus maximus by squeezing them tight as possible to maintain squared hips and pelvis.
Now, internally rotating, retracting and depressing your right shoulder while pronating your right forearm bring your right arm around your back to grasp onto your right foot.  This should be easy.  This is working your teres major, and infraspinatus muscles.  To make this easier bring your vastus lateralis into a stretch so that the knee faces the floor.  Your hand should in effect hold your foot in place.  Flexing from your hips fold forward into the sagittal plane a much as possible.  Your iliospoas, pectineus, and tensor fascae latte should all be flexed.  Lengthen your spine by aiming your head to the floor.
Prior to performing this pose it helps if your hamstrings are warm and loose for flexibility.  Anterior deltoids, and loose shoulders are needed as well.    Strength of your hip flexors are needed along with the strength to contract your diaphragm.  The Marichysana poses are good warm ups.  Prasarita Padottonasana A & B along with Purvatattonasana are also good warm up poses.  To improve on balance one should do the tree pose.  To improve on this pose try starting by doing it in a seated position.