How To Create Shadows
To create shadows on your canvas, you must first pick a light source on your canvas. This can be either on the upper right or left corner on the canvas. Remember, light usually comes from above.
Trace the object on tissue or velum paper. Move the paper to the opposite side of the light and just below the object. This is creating the shadows.
Here is the end result. Remember to use darker values for shadows and lighter ones for highlights.
The following illustrations will help you in your shading.