The rule of thirds. The rule of thirds draws the subject away from the center of the photograph. You can imagine it by thinking of the image cleaved in nine equal segments by the help of two vertical lines and two horizontal ones. According to the rule of thirds, you should place the most important part of the photograph along the points where the lines cross. This creates balance in your photos and livens it up.
Many cameras even have the option of an imaginary grid that is superimposed on the LCD allowing you to take the perfect shot. This makes it very easy to follow this rule and take great pictures.