CJ, I agree about clutter. Nothing like clutter to ruin a potentially good picture. That's why we spend time in Photoshop removing it if we couldn't avoid it in the first place. Good rule to remember.
Phoenikz, I agree that timing is another very important factor. It's very important in pictures of people (for expressions) and of animals, especially moving animals, especially flying birds! Here is my favorite "bird in flight" pic on PBase so far. http://www.pbase.com/image/15255906 Not a majestic eagle or graceful swan, but just a little short chubby gull. What makes this photo outstanding is not the subject, but the grace of the wings and the perfect timing of the shoot. Also has good composition and delicate shading/color and technical details of focus and exposure etc. Hard one to beat! It belongs to Bill Pruitt...check this same gallery for other examples of great timing, such as a stork poised in mid air about to land on its nest, a pelican "leading an orchestra" etc.
Timing applies of course to all action shots, and thankfully we no longer have to waste a roll of film to get, maybe, one great shot. Here is one that required amazing timing or a camera set on "burst" shooting or both. http://www.pbase.com/image/22572261
But remember that timing is also important for getting that "adorable expression" on a baby etc. Oh, for a second chance at the ones that got away!