Update: Since this was published, Google has disentangled Hangouts on Air from Google+ and rebranded the product YouTube Live. See my updated guidance: Creating a YouTube Live Event, with a Landing Page on Your WordPress Website.
The tutorial I recommend on how to run your own Hangouts Q&A session is here:
Thanks to Jim and Chris Guld of Geeks on Tour for joining me at the end of the show. Look up their next event or watch one of the replays here: