To balance on one leg requires steadiness, stability (sthira), which in part comes from strength by engaging through the appropriate muscles on the standing leg. The action of pressing the raised foot into the opposite leg, and the leg pushes back into the foot, is a more yang action.
But it also requires some openness and mobility in the hips, to be able to turn the knee out without the hips and pelvis coming out of a neutral alignment.
We seek ease in the upper body: keeping shoulders down when hands are in prayer position, or even if elevated to raise the arms above the head, we still want to have relaxed shoulders and easy breathing. It helps to think of the upper body as the spreading branches of the tree: they may sway and float in the wind. Whilst the legs are the trunk: solid, grounding, reaching down into the earth.
Whilst good for building balance, it is also building muscular strength in the hips and legs when you engage the muscles in correct alignment.
Bring your right foot to the inside of the left leg. If your balance isn’t great you can keep the ball of the foot on the floor and bring the heel to your left ankle. Otherwise to the lower or upper leg, preferably above or below the knee joint so that you are not putting pressure there.
Keep the pelvis in a neutral alignment. The hip bones should be even, don’t let the standing hip sag out to the side or the opposite hip drop. Also keep hips pointing forward: as you turn your right knee out, don’t let the pointy hip bone follow and turn to the right; keep both pointing forward.
Press firmly into the standing foot but lift through the inner arch. It helps to visualize that your breath enters through the sole of your foot, so that as you inhale your breath travels up your leg, drawing the arch up with it.
Arms can take numerous versions: in prayer with hands in front of the chest or above the head, hands wide above the head, or reverse prayer or take opposite elbows behind the back.
Keep the belly contained; lift it in and up and keep the front ribs drawing together. The hip bones are lifting towards the bottom ribs and the tailbone is descending.
Stay for as long as you can. Studies have shown that we start to lay new bone once we have been standing on one leg for 112 seconds!