Perceived depth in a photograph is a key element in successful and beautiful photography. This is particularly important with three dimensional objects. To help us understand how we can use light and shadow in our photography there is no better place to start than Chiaroscuro. This concept and technique really took hold during the renaissance in drawing, and then later in woodcuts and then into paintings.
Personally I think you should study Caravaggio as the ultimate master of this technique. Photographically I would suggest you drop in a explore Bill Henson's work as a modern master of this form of lighting and moulding or three dimensions in figurative photography.
The classic method of learning about this is to start by photographing eggs on an off white background. Explore using various lighting until you can create a strictly three dimensional representation of a spherical object. What you are looking for is crescent shaped shadows. Crescent shaped highlights. Full rich blacks, and full rich whites, and every tone of grey in- between.
Notice in the example shown, we have paid special attention to putting a lighter tone next to a darker tone to help with the illusion of depth. The tiny light on the left hand side of the sculpture is very delicately controlled to create a separation of the head from the background. Notice there is none on the other side of the head.
For a challenge photograph something spherical and white, such as eggs or a bowl or even a porcelain figure. Use strong directional lighting and create an image that has depth that is created through the use of light and dark. Stop and research Caravaggio's paintings, and figure out how you might incorporate chiaroscuro into your photography.