mastercopy after steve huston i did about 2 years back using compressed charcoal.
I learnt alot of information from this teacher especially his teachings on gesture and structure and how to maintain gesture when rendering drawings to a high level of finish. Strip away the fancy rendering of light and shadow and the drawing is essentialy a simple communicated construction. The trick is to be able to break the model down into these simple ideas. Ive been looking alot of 'disney' animators drawings of late and them guys knew how to simplify and communicate through gesture and structure. As easy as it looks its much more difficult to simplify as you are translating the model not copying it.