This lesson (written by Kevin Ferrara) any photographer should learn. There Kevin teaches us about meaningful composition:

By "meaningful composition" I mean a composition that is "abstractly informative in a psychological or symbolic way". So what elements of a composition can be "abstractly informative in a psychological or symbolic way"? In short, just about anything related to the craft of composing pictures: The Shapes, the Lines, the Colors, the justaposition of elements, the framing, and on and on. Everything except the subject matter, which is real or "concrete", not abstract. "