Very bad tutorial...
But nice design. The first step to teaching shading is ALWAYS telling people to use one light source to relate all the shading around. Your "Line Shading" of the box isn't correct; the top side of the 3-D box isn't even shaded with the same light source of the other side. Your "Shrinking and recoloring method" example was what really ruined all hope for the usefullness of this tutorial. You my friend have just shown everyone how to pillow shade, a very bad technique of shading. Pillow shading is were the light source of your object is seemingly inside the shape (with it's lightest point being in the middle and it's darkest at the edges). The only time pillow shading is realistic is when the object is a source of light such as a light bulb, or, assuming that your "ball" is a sphere, that the light is coming straight from the viewer. This is all kind of hard to explain without pictures. Anyway, as I said, nice design on the tutorial I just wished you were a little more informed on the topic.