The rule of thirds is a composition principle found in design-related fields including:
If you're a photography buff (beginner or pro) you can gain more insight into the rule of thirds by browsing this gallery of rule of thirds examples from our former About.com Photography Guide Liz Masoner. Practicing with the rule of thirds whenever you snap a photograph can help you in utilzing the rule of thirds when composing page layouts with or without pictures.
You can also employ the rule of thirds on photos that might have less than ideal composition during photo editing. About.com Graphics Software Guide Sue Chastain demonstrates the rules of thirds and cropping.