When I did my B&W bust I followed the technique of Ansel Adams, photographer known for his B&W subjects. He would make sure that he used the entire "spectrum" of "colors." So part of the figure should be pure white, and another pure black. Then create your gradients. Not much help but there it is...
Kev and Beave - I guess I was just thinking to start with with white of light gray and go to black because darks cover lights better than lights cover darks. I'm lovin' the Ansel Adams theory, Kev !!