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!