In a shot with glasses, avoid reflections – and it is easy. Move the lights (umbrellas, softboxes, whatever you use) 45 degrees to the subject’s side, and 45 degrees up.
If you see a reflection, like this:
..then do the following:
- move the lights a little further up
- or ask the subject to aim his head down just a little.
And often, “simple” is all you need. Just remember to pay attention to possible reflections!