RDO just had our second Google Hangout On Air event, and it went much more smoothly the second time around, now that we have some idea of what you're doing. I wanted to share a few things while it's still fresh in my mind. Because of the way Google Hangouts work, there are several things that are not exactly intuitive, and you need to plan ahead for best results.
I don't have any illusion that I'm an expert, but hopefully these tips will help you be successful if you do your own hangout. I would appreciate your feedback and additional tips.
Attendee Limits and Hangout Tips
Hangouts have a 10 attendee limit. We found that out the hard way the first time. So your audience doesn't actually join the hangout. Instead, they watch a live stream on Youtube, where there's no limit. Don't invite people to the hangout unless they are actually going to be talking.
You can schedule a Hangout, but you cannot schedule an On Air Hangout. Don't get confused and schedule a Hangout and then have to change it later on. That'll just lose you half your audience.
Camera switches on voice - that is, the person talking gets the camera. So if you're not presenting, mute your microphone so that it doesn't suddenly switch to a shot of you cleaning your ears when you happen to rustle a paper. Better yet, turn off your camera, too, when you're not presenting.
Test Ahead of Time
Presenting in a Google Hangout requires plugins, and the controls aren't immediately obvious. Create a test On Air event and have the presenter join and share their slides. It can be weird talking to your screen for an hour without seeing the audience, and it can be doubly flustering if things don't work quite how you thought they would. Give them the option of doing a full runthrough if they really want to, but at a minumum ensure that they can join the test hangout and get their slides shared, and that their microphone works well, there isn't a terrible echo in the room they're in, and so on.
Timezones suck. Use TimeAndDate.com to create a page that shows everyone the time in their own timezone, for example http://www.timeanddate.com/worldclock/fixedtime.html?iso=20131031T1600
Youtube Stream URL
The event that you've created in Google Plus, and the actual "On Air" event, are not connected to one another in any way. You need to create an event, and then put the URL of the On Air event in the description. Unfortunately, you can't schedule the On Air event ahead of time. So you create the On Air event (ie, Youtube stream) and then edit the description 20-30 minutes before you're scheduled to start.
Start the On Air event well in advance and share a window (LibreOffice Present?) with details about the hangout and when it will start. You can edit that bit off when you're done, so that it's not in the final video.
What I'm going to do next time is have placeholder page for the weeks leading up to the event. Then, the day of the event, create the On Air event and redirect that URL to the event. Of course, to do that, you'll need to have a server where you can redirect URLs, or a URL shortener that you can update, or something like that. Failing that, just update the Google Event when you have the Youtube URL, or perhaps publicize a blog post or forum post which you then update with that URL.
Q & A
Although the Hangout has a Q&A tool, that's only for people that are in the hangout. I'm still looking for a good Q&A tool, but for now we're using IRC. I recommend that you create a new IRC channel, rather than using your existing one. This removes the off-topic chatter, and makes it easier to have a transcript and an attendee list.
For the many people who are not comfortable with IRC, give them a web link, like https://webchat.freenode.net/?channels=rdohangout which takes them directly to the web chat applet.
Once the event is over, Youtube has a simple edit tool that will let you trim off the 30 minutes of dead air at the beginning of the recording. This takes a LONG time, so make sure it's done before you start publicizing the URL of the video.
If you have any other tips, please share them with me. I want the third one to be even better than the second.