This isn't a post about how to walk down stairs, don't worry! By stairstepping, I mean a way to see subforms on any shape. This way of seeing forms is based of the simple shape of stairs, and when taken to a more sophisticated level resembles the ridges and steps in a shale rock face. One of the artists who most clearly uses this idea is the american illustrator Dean Cornwell. His drawings show this very clearly, and he uses this in his paintings as well, but blends the simple geometry more to create a more finished realistic look.
The basic concept is to imagine a tubular or other basic solid and then carve steps into it that will be in shadow. This technique is great for all sorts of subjects such as trees, rock, buildings and the shapes on an animal or human.
Below are some of the basic steps of this technique as applied to a human figure: