Learning

There are three things one has to do in order to become a decent photographer:

1) Take a lot of photos
2) Look for reference and inspiration in books or exhibitions by (good) professional photographers
3) Learn the essential rules of composition and design

I believe the last item is often neglected. We tend to rely on our sensibility and good taste, often forgetting that a good composition actually obeys to some well known "laws" that the master painters of the Renaissance new so well. One way to study this is Michael Freeman's book "The Photographer's Eye."

Freeman is a professional photographer and author of many books on photography. I still have his "35 mm Handbook", which I found very useful in my beginner years.
"The Photographer's Eye" is a more "theoretical" approach to photography, presenting a systematic view on the different "non-technical" elements that contribute to a good photograph. It is clearly written and full of excellent examples. Periodically I reread parts of it, trying to better assimilate the concepts, hoping they will become a natural part of my "photographic process."