Definition: When cropping a photo, it is a good idea to follow the "rule of thirds." With the rule of thirds, you mentally divide the crop area with two evenly spaced vertical lines and two evenly spaced horizontal lines, creating a grid of nine sections. To create a pleasing composition, the primary focal point of the image should fall at one of the line intersections. (Continued below...)
Avoid placing the focal point in the dead center of the image as this generally creates a bland composition. In a horizontal arrangment, the horizon line should be placed along one of the two imaginary horizontal lines, and in a vertical arrangement, the subject should be placed along one of the imaginary vertical lines. When possible, also strive to have you subject facing into the picture.
Microsoft Digital Image Pro is one software application that helps you improve your compositions by employing the rule of thirds in the crop tool.
As with any rule, there are exceptions, but if you keep this guideline in mind, your photos will likely seem more interesting. One situation where you should avoid the rule of thirds, is when you want to emphasize a pattern.
Rule of Thirds and Visual Center
A mini-class from About's Desktop Publishing site discusses the rule of thirds and how it can help you create better layouts.
The Golden Ratio in Design
Explore the mathematics and the art of the Golden Proportions and the Golden Rectangle, especially as it applies to paper sizes, page layout, and graphic design.