The Rule of Thirds is a rule of thumb...

The rule of thirds is a photography "rule" that suggests you should envision your scene divided into 3 horizontal and 3 vertical divisions . Common thought suggests that placing a subject on these division lines creates more drama, or better composition. A common application is shooting a sunset. Many times our brain tells us to center the horizon line in the frame. However, you can capture much more of a beautiful sky just by tilting upwards and placing the horizon at the bottom third of the image.

The four points where the lines cross are sometimes called "power points" and are great places to place your subject. Many times a portrait will have a person's body in line with a vertical line and his/her eyes in line with a horizontal line.

Subjects do not have to follow these lines exactly, even placing the subject in the general area of these lines can help composition. And as always, rules are made to be broken, so if you don't like the way the "rule of thirds" makes your shot look, then ignore it, after all, it's your picture!