The Rule of Thirds is simple really – the idea is that you place your subject or main point of interest in one of the four points created when you cut an image into thirds or on the third lines.  Lets use this image of a butterfly I took to see the different it can make to the composition of an image by the position of the butterfly.

In this first image the butterfly is not on any of the lines or intersection points

By repositioning the butterflys head at one of the intersections and its wing on the line of the third a much more pleasing aesthetic is created.

Here are a few examples where you see photos compositions is based on using the rule of thirds.

Other posts on Composition:
Simplify Your Subject
Leading Lines & S Curve
Beware of Mergers
Symmetry & Balance
Cropping
Composition Printable