How to take photographs of people wearing glasses
Photography blog, Strobist, recently posted about taking photographs of people wearing glasses.
The entry features this video by photographer, Craig Burfoot.
It's mostly a matter of common sense and trial and error. In the video, the photographer has fancy studio lighting, but the advice could easily apply to cheap light sources such a lamps or where you place your subject in relation to the sun. The comments on the entry are very useful, too.