Perspective with a twist. Take any food item (preferably something you would like to eat) that is also amenable to drawing in one, two, or three point perspective. Render value gradations to produce a range of values from very light to very dark (shading). Render your value gradations with a defined single light source. Place this object into an environment, real or imagined. No more than 70% of the picture may be rendered (plan in advance where you will leave white space).