Once you're in the shape of the pose, use your awareness to refine it. Become like an aja, a mountain goat, sure-footedly dancing across the rocks. Tuck your tailbone down; draw your lower ribs back. Feel your legs, buttocks, and hips nimbly follow that goat as it leaps high to impossible precipices, and deftly steps down to narrow ledges below. Wherever you go, your thigh, shin, and knee should support you. Start by drawing your inner legs together; then press them apart. Next, partly straighten the right leg, angling it slightly out. Gently push toward the wall while resisting slightly from the hips and torso; then gently push away from it, again resisting slightly. Now angle the leg slightly in and repeat. Experiment with the placement of your knee and notice how the movements affect the surrounding ligaments as they respond to the movements of the hips. This is going to be a vital skill.
Never, however, endanger your ligaments by subjecting them to too much stress. When your "inner goat" has played upon the mountain long enough, come out of the pose by placing your fingertips on the ground, leaning forward, and removing the left leg from the wall. Then repeat the pose on the other side.
In addition to strong, resilient legs, there's another secret to Natarajasana: long, strong hip adductors. The adductors are muscles that live deep within the inner groins and run along the inner thighs. Larger than the hamstrings and almost as large as the quadriceps, they are capable of many tasks: They draw the thighs together, rotate them, extend the hips, and help keep the pelvis level, steady, and balanced, particularly when you're standing on one leg. But in most people, they are tight and weak and get less attention than the quadriceps and hamstrings.
If your adductors aren't long or strong when you try to lift a leg up and back, as you would in Natarajasana, you'll lose your balance or overbend your lower back. And while there's no denying that the lower back needs to bend in Natarajasana, overdoing it is the surest way to create compression and injuries there. The more you can hollow your groins, the less stress you'll place on your lower back. The word "groin" comes from the Old English grynde, meaning abyss, so think of creating an abyss as you draw the adductors back.
To lengthen the adductors, practice these versions of Baddha Konasana. To begin, sit on a block. Exhaling, bend your legs, separate your knees, and draw your heels as close to your pelvis as is comfortably possible. Press the soles of your feet together. Before you fold forward, be like that mountain goat who jumps nimbly up before descending the mountain. Feel your torso lift and lengthen as though you were coming up and over your hips, then exhale as you incline the torso forward.
Move from the hips, not from the waist. Use deep awareness to fully contact your inner thighs with your mind and your breath. Continue lengthening the torso while you ease the femurs sideways, away from the hips. Never force the knees: They should always follow, and never lead, the slow releasing of the thighs. Stop immediately at any sign of unease or weariness. After several breaths, inhale to come up. Then turn very slightly to the right, lengthen away from the left inner thigh, and fold forward. Hold this for a few moments, release, and repeat to the left.