I think cropping is a valuable tool, especially when looking through old photos. Concentrating on one particular area can completely transform and strenghthen an 'average' looking photograph. Im not sure of any specific technique, but I tend to just try different crops and go with the one that looks and 'feels' right (if any!!). I think one of the most important things is to look at your background and ask yourself if it adds anything to your subject, does it tell a story? I find this quite challenging sometimes. Saying that, I'm now trying to take more time when actually preparing for the photograph so that I get in right 'in camera'.
