Hello! I would recommend starting out with line drawings to directly practice structure before going on to shading to keep things simple, but good job breaking things down to simple forms. Hampton starts out with a gesture or "envelope" shape, and I think this would help you get the flow and curvature of the feet, as it currently seems rather uniformly boxy whereas the reference pose accentuates the arch. Also, don't forget the "ball and wrench" shape that he uses to indicate the ankle and transition into the lower leg. Here's a quick sketch I hope helps: