Natasha's reply:Dear Elizabeth,
When I teach Virabhadrasana I (Warrior I), I usually begin by emphasizing the back leg and foot. Then, as the student begins to get warmer, I add the rotation of the hips. There are a number of reasons why it's hard to keep the back foot flat and revolve the hip forward, but one of the biggest culprits is a lack of flexibility in the ankle and the Achilles tendon. It's important, therefore, to work the feet very thoughtfully so that you can develop your range of motion in these areas.
My suggestion is that you initially back out of the pose by straightening the front leg a bit, so that you have a better ability to anchor the pose through the outer edge of the back foot. Once you have established a certain heaviness along this outer edge, see if you can lift the inner arch and inner ankle to further emphasize this state. Then see if you can translate the lift in the inner arch into a lift and spin back with your inner thigh. This internal rotation in the back leg will help you rotate the back hip forward.
Stabilize the action of the back foot by pressing back very firmly with the top of the back thigh, so that you can really root down with the outer edge of the back heel. Then, without compromising the work in the back leg and foot, slowly begin to bend the front leg, moving toward a right angle but stopping when you start to lose the integrity of the back foot. Ironically, the more you can connect to the floor with the outer edge of the back foot, the more you will be able to create the lift and spin in the inner foot and thigh that will facilitate the action of the hip.