Here's some tips on running games over Google+...
1. Start at a point where the players get to do something.
Please. Please do this. Please. Please. Please. Please don't ever not do this. Maybe a little infodump first, but do not make people go through any pre-conceived motions. Hangout games are relatively short, play time is precious and someone always has to go to work in 2 hours.
2. In scheduling hell? Pick one person and have them assemble a team of players. Or just say "whichever team assembles itself gets scheduled"
3. Creating a "Google Plus Event" seems like a boring, redundant thing to do, I know, but the nice thing is it automatically adjusts the time to each player's time zone.
I play with Australians.
4. 3-4 players, one GM is perfect.
More than that and you have to start choosing between the amusing cross chatter and the actually getting the game to move forward.
5. If you are running a game with like 8-9 people, clear, simple objectives immediately are helpful.
You're in a dungeon: crawl it. There's a contest: win it. There's an NPC: talk to it. Etc.
James Mal manages to run a pretty big game smoothly by going "Ok, you're in Dwimmermount, play the game".
6.Seriously, you can explain the mechanics as they come up during the game. It works fine. Front-loading the players with stuff they don't need to know is just sucking away time you could be using to play.
7. Do not send the campaign materials.
"Ok, I'll send you the campaign materials" Please Christ no do not do that. Let me play a session first and let me decide I care about your setting before asking me to read a novella about it. Srsly yo.
But you love your campaign materials, I know.
Look at them, imagine someone not reading them. Then think of the very important play opportunities they will be missing if they do not read them. Are there any, really? Then find a way to work those things into the first session. Anything else supervital should be able to fit into a sentence or three. If you have to.
8. If it's a system your players don't know, make a custom character creation doc and make it short.
Nearly every RPG has an obnoxiously bloated stupidfatlong character generation section that sucks and was obviously written by drunk lemurs who skipped school a lot. And it definitely wasn't written with your setting or house rules in mind. Write a thing.
9. "Player Cloud" campaigns are fun and work.
So you want all your friends to play but scheduling is a Lovecraftian nightmare and besides, if everyone showed up you'd have too many players. Try having a lot of players in the campaign but only a few of them per session.
So far on G+ it's worked out really well: you put up a short play report everyone can see, players ask each other questions and kibitz, information gets traded, it works out. Your game is a bar, the players are the regulars, sometimes this guy is there, sometimes that girl is there.
This beats splitting your game into two non-overlapping groups and beats it hard enough that it may well be worth re-arranging your game structure a little to accommodate the drop-ins.
10. You don't have to ask a million questions first
High fantasy or low fantasy, guys? Basic or advanced, guys? Should there be kobolds, guys?
Exactly what kind of game do your players want? Whether they know it or not, they probably want to run the campaign you're most excited about. Honestly: we might have slight preferences, but we have no idea, do what you're good at. Do your thing as well as you can, ask your players questions about how it's working after they've seen how you run it.
11. If you need players, use the Constantcon Blog and the attached calendar.
12. There are lots of fancy aps you can run over G+. Do not rely on them, they can easily break half your players' connections.
Test your widgets some time when you're not running a game. Adopt it once you're sure it works.
13. The Screenshare button works fine and is usually the simplest solution.
That button that says "screenshare" on the upper left will allow you to show the other players contents of any window you have open on your own screen. It will appear where your head would normally be. It'll show it in real time, so if you are building a diagram in photoshop or something, the players can watch. It also stresses the players' connections out way less then having them downloads aps or visit links to see pictures or diagrams.