Mitch Alland, a recent convert to street photography, has written a thoughtful article on the subject on his blog, The Online Photographer. Good stuff, debatable thoughts such as his feeling that you need a project in order to be a better street photographer. Not how I learned it. My motivation is to see what things look like photographed, in black and white, and how the framed two-dimensional image freezes and transforms a moment.
Of course, it has to be interesting, and there has to be a tension between the form and content of the image. Visit his site to see some really good work.
In any case, this is a good read, as are the reader comments at the end.