Every photographers serious about their composition would understand the importance of "The Rule Of Thirds".
If you don't, listen up ;)
So what is this "Rule"?
Wikipedia described this powerful technique to make your photos more interesting as:
"The rule of thirds is a compositional rule of thumb in visual arts such as painting, photography and design.
 The rule states that an image should be imagined as divided into nine equal parts by two equally-spaced horizontal lines and two equally-spaced vertical lines, and that important compositional elements should be placed along these lines or their intersections.
 Proponents of the technique claim that aligning a subject with these points creates more tension, energy and interest in the composition than simply centering the subject would."
Confused? Take a look at the diagram below...
Put it simply, the rule of thirds says that your picture is most interesting when its subject is composed along imaginary lines that divide the photo into thirds, vertically and horizontally.