>>18193919If you're shading you have to think about the shape and curvature of the face or object. The shadows will always be consistent with the direction of the light source too. Notice how you can easily tell where the light is coming from in these photos despite there being shadows all over the faces. Also if you want to go more detailed then think about highlights. Notice how bright parts of their noses are for example.
But this is all probably too much details for 'jaks which are more flat and simple, but still worth practicing.