Composition Expert

Rule of thirds
The basic Principals behind the rule of thirds is to visualize breaking down an image into thirds (both vertically and horizontally) so this gives you 9 slots like the example below;

The theory is that if you place points of interest in the slots then it makes the shot look a lot more appealing as none of the slots are empty, because if they were then the shot would look out of place and dull in certain slots. It just makes sure that the things that you want to capture the viewers eye is on eye level for example;

Here the eyes are on the top line for primary interest and the tie and flowers and of secondary interest and they are on the lower line.