What's the rule of thirds?

[J.J.]

What's the rule of thirds?

[alistair]

Use imaginary lines one third from the top and bottom of the viewfinder image and lines one third of the way in from the left and right.
Place important elements where these lines intersect for easy/attractive composition.
For a bit more detail and a wee diagram look here:
http://www.silverlight.co.uk/tutorials/compose_expose/thirds.html