One of my favorite Yoga asanas to do is Dancer's Pose or Natarajasana.
This pose helps to create mental concetration and of course balance. It's a great stretch to open the hips, leg and thigh as well as the arm and shoulder and helps to tone the legs. Dancer's Pose strengthens the spine and the entire leg.
From Mountain Pose, concentrate on a spot a few feet ahead of you on the wall. Take a deep breath and ground yourself down into the standing leg, while you lift the other leg. Drop one hand (the same as the leg you are lifting) down to your side and grab a hold of the ankle of the foot you are lifting. As you exhale, slowly tilt the body forward while pushing your leg up into the air.
I need to work on getting my leg a little higher in the air! Ideally your arm and leg (where the knee ends/folds) should create one long lean, straight line.