There are two sides to dealing with value.
1.Value as an element of rendering/realism: Chiaroscuro.
2.Value as an element of pure design: Notan.
Chiaroscuro (light-shadow) is an oil painting technique, developed during the Renaissance, that uses strong tonal contrasts between light and dark to model three-dimensional forms.
The underlying principle is that solidity of form is best achieved by the light falling against it. Artists known for developing the technique include Leonardo da Vinci, Caravaggio, and Rembrandt. It is a mainstay of black and white photography.
Whereas the Japanese technique of Notan exploits value almost exclusively as design element. The Italian technique focus's on value as a rendering element to heighten realism.
A great piece of modern design/illustraion work typically demonstrates mastery of both Notan and Chiaroscuro.
Chiaroscuro (light and shadow)
The first step to mastery in your understanding of light and its effects on various surfaces is to understand how light effects these basic forms. All other, more complex forms can be built from: cubes, cones, cylinders, and spheres....
C. Core Shadow
D. Reflected Light
E. Cast Shadow
Different materials reflect light in different manners and must be rendered accordingly! Avoid making work where every surface is rendered exactly the same.
Various Metal Cylinders, Cones and cubes: Notice that the specular highlight and core shadow not only elongates across the the entire span of the cones and cylinders but that they also rotate with the object.
If you can render basic shapes you can render anything including the human form.
If you can paint a sphere you can paint a butt. ;-)
Advanced lighting note....
-Every plane change has a value change....