Identify the major shapes.
Observe the value relationships between them.
Take the shortest route to a clear and simple realization of the light/middle/dark pattern.
For homework, look for an image that displays the clarity of a strong value pattern. Do a very quick study, giving emphasis to shape and value, with the merest nod toward texture. Below are a couple of possibilities. If you use one you find yourself, please bring the source image along to the next class.