Design Principles

Rule of thirds:

http://gizmodo.com/5875104/shooting-challenge-rule-the-thirds

Symmetrical:

 http://www.math.brown.edu/~banchoff/Yale/project04/bio.html

Asymmetrical:

 http://justinealegre.wikispaces.com/What%27s+my+line%3F

Radial:

http://www.flickr.com/photos/61024080@N00/389709552/