I think that it's about following two or more conversations at once. Listening without trying to figure out what exactly to say. When one group's conversation draws you in bring your attention there. And like a one on one conversation, when you've something to say, say it. Center yourself and don't try to force it. If you aren't the natural gabber, don't worry about trying to become what you're not. A smile. A knodding of your head. A laugh or a chuckle.