Glass tabletops, when lit from underneath, make excellent tracing tables. Simply situate a lamp underneath the glass surface, place your sketch on top of the table (tape it down if need be), and place your blank paper on top. With adequate lighting, you should have an easily visible sketch to work on top of.
I like to use this method when transferring to-scale sketches to Arches Watercolor Paper. Note to self : change that lightbulb to an energy efficient one!
Note : Be careful of overheating, as a hot glass surface can be dangerous / crack.