Ok how to show that. If you look at comics, the shadow area is flat black. It does not have to be black, but it has to be flat, as in little activity or contrast. In the lit areas, you can have a little lighter and darker to show smaller more subtle forms. But here is the point often missed- keep the shadow and lit value SEPARATE. Thou shalt make no value in shadow lighter than the darkest area of what is in light. Read that slow. The shadow has values in 2-3-4 and light has values 7-8-9, if you think of white as 10 and black as 0.
So apply this thinking front planes of the body in shadow, side in light.