I did on Broadway a year ago, so here are some ideas thatI recommend:
-Pick a composer and talk about all their shows- musically, thematicaly, etc.
-Talk about shows that were not huge sucesses when they first opened, but are now considered masterpieces today and why people's opinions have changed
-Simularly, talk about shows that were huge sucesses but are now hated by most people today (Annie, for example)
Everyone else who has already posted also has great ideas. I agree, music is crucial to the presentation, so have a cd to play.
There's a lot I am not certain of...