I can give you some tips on shading. You must know from which direction your light source is coming from, it helps to put a small dot there. Then place the darkest shadow under the object, if the object is on the ground or table, from the opposite side from the light.Next place the darkest shadow on the object itself, again opposite from the light. You want to build up your shadow to become lighter as you get nearer the places the light is hitting. Finally you can even erase the outline where the light is directly hitting the object. Hope that helps a bit. Study everything you see to give you lots of into on where shadows are and how long they should be.

Thx