Contrast is one of the most important concepts in photography and design. Having appropriate contrast in your frame, either through lighting, color, or size will draw your viewer's eye to your subject. It takes a bit of practice and experience to master how to use this technique but over time you will start to "see" it through your viewfinder. In the photo above, the stark difference between the black and white parts of the frame draws you directly to the photographer at the center.
