Rule of 3rds - an off-centre composition is more pleasing to the eye and looks more natural than one where the subject is placed right in the middle of the frame. It also encourages you to make creative use of negative space, the empty areas around your subject.
Photo Essay - http://time.com/3687500/photojournalism-links-january/Articles to read:
- Horizontal = stability
- Vertical = power/ strength to growth
- Diagonal = adds action and drama by creating points of interest for the eye
- Converging = adds interest by drawing the eye in