Composition was our chief topic this week. We discussed the basic rules of composition and looked at examples of each, but French photographer Henri Cartier-Bresson was looked at in-depth. Other photographers who we talked about or looked at were David Alan Harvey, Susan Meiselas, Alex Webb, Sam Abell, and Alfred Stieglitz.
Cartier-Bresson's best known book where the phrase "decisive moment" was coined is available here as an e-book: Images a la Sauvette.
As I said the composition can get quite complex and some sources get awfully detailed. Here are a few places online that simplify it into easy-to-understand ways.
Rule of Thirds
Leading Lines
Simplicity
Framing
Balance
Avoid Mergers
Point of View
Kodak keeps it incredibly simple as well with a list of six basic rules: link.
This website is aimed at flower photography, but the rules are essentially the same and can be applied to other genres of photography. It's simplified and in PDF form for easy printout: link.
Here is another good list of rules on PDF for easy print out: link.
For more detailed look at the elements of composition, Arnold John Kaplan goes in deeper.
This one by Theresa Husarik is simple an fun: link. Another on the same site by Peter Saw is aimed at painting but fun in a simple, yet detailed, slideshow form: (Incidentally, there is a great selection of articles on composition on photoinf.com.
Wikipedia can be sketchy but it has its strong points. They have a good detail of rules of composition that apply broadly to photography and visual arts: link