You can pick any structure, but this one seems to work well.
1. Put up a post saying that you are going to have a writing date at [x] time OR just spontaneously open a hangout.
2. As soon as the hangout is open, place a comment on it that states that it is a writing date and what the parameters are.
3. Suggested parameters: “We’ll chat for fifteen minutes. Then at quarter past we’ll start writing for forty-five minutes. On the hour, there’s another 15 minute break for chat… Rinse and repeat. If you want to join in mid-way, that’s fine, but we’ll just wave at you until the next break.”
4. Continue until you need to log off. If the other participants are still going, they will be able to keep writing after you leave.
While I find it difficult to stay with a writing hangout for an extended time because of my home schedule, I do find it's exceedingly motivating just to pop in, and each time I have, I've gotten a little writing done during a time that I would ordinarily have accomplished nothing.
I'm also exploring these hangouts as a place to conduct post-critique discussions with my online-only writer's group, Written in Blood. Our technique for critique is to do one story at a time with a short window for reading and critiquing, and then to conduct a discussion after the recipient has received all the written critiques. The next time someone submits a story, we're going to be scheduling a Google+ hangout so that we can have the post-critique discussion in real time. I'm really looking forward to it, because I find that questions and discussion flow a lot more easily in face to face contexts, and we'll be able to do more helpful brainstorming for our members, at the same time that we'll be bonding socially and creating a better rapport between members who live in wildly disparate locations.
I'm also thinking about hosting an experimental hangout session to discuss worldbuilding and language questions. If you'd be interested to participate, comment, and I'll post a time to give it a try!
Update: I'll be holding the session next Wednesday (Worldbuilding Wednesday!), July 20th, at 10am PDT. We'll see how the discussion goes, but it might be great to segue into a Mary-style writing hangout at a certain point, too.
Have you had any new ideas for Google+ hangouts? Have you had a good experience with one that you'd like to share? Tell me about it!