Spectacles and Portrait Photography
If the subject normally wears spectacles, leave them on - they are a part of the persona. To avoid bad reflections reposition the light source and/or face to avoid specular reflection. Remember light only ever travels in straight lines so if the angle from the spectacle surface to the light is DIFFERENT to the angle from the spectacle surface to the camera you should have no major problems. Some reflection is normal and a part of the portrait. SLR cameras are best for viewing because what you see is what you get. Avoid using on-camera flash not just to avoid reflections but to avoid all the other negatives associated with on-camera flash.