Lighting 101: Lighting for Glasses
But if glasses have been giving you a Devil of a time, this is gonna be one of those Homer Simpson "D'Oh!" moments. And if you are having trouble with it, don't feel bad. I did, too.
The problem is that if you are going to the trouble to light someone, you are naturally inclined to have them face toward the light. Which is fine.
Unless they are wearing glasses.
To avoid refections in glasses, simply light from one side and have the person face the other. There is no need to be shooting all of the way in profile, either. A flattering, 3/4 angle (subject to camera) will work just fine.
Think of the light hitting the glasses as a pool ball. It's going to reflect off of the glasses, no matter what. The thing is to position the glasses so that the angle is such that the light reflects harmlessly off into space. Doesn't really matter where. Just not towards your camera.
If the subject is looking away from the light, that's a piece of cake. That's all there is to it.
Next: Lighting 101: Long-Throw Hard Light