Today our models were Patty Arquette, Valentino, Max and Oliver Twist. For a short demonstration I did this drawing and drew lines around the major highlight and shadow areas. Many artists do this as a way to establish the over-all highlight and shadows before getting to more detail. In addition to keeping track of the big picture it has the added benefit of giving you more shapes and points of reference to use as you make the drawing. After drawing lines around the major highlight and shadows I filled in those areas with a fairly even covering of white and black charcoal. Only then did I start adding more specific highlight and shadows on smaller areas.
In the first few minutes of the video below you can see a much more thorough demonstration of what I was talking about. He talks in terms of primary, secondary and tertiary forms while I tend to think of it in terms of "global" highlights and shadows vs. "local" highlights and shadows. The point is the same - you've got to establish (and maintain) the big picture before you get to the details.
Next week our model will be David Abercrombie and we will have one long pose for the entire class. This will be a great time to bring your paints.