Something I've seen a lot of guys do: if one guy makes an interesting comment to the more outspoken guy, then the outspoken guy steals the idea and loudly says it to the whole group. I don't really like doing that, I prefer to create my own ideas.
I think there is a dynamic that is usually set very early in a group of dominance. Once you establish that dominance, you'll generally find it easier to keep it. But it can work the other way too. Sometimes I don't say much for whatever reason and some guy will try hard himself out. Then the nexy thing you know the chick is trying to get rapport with me, and I really haven't done much. I just didn't show immediate interest, waited for him to tryhard out, then when she turned her attention to me I slowly started responding.
In general, because most guys come across too "flat", boring, shy, and insecure, I'd say it's better to try overtalking than undertalking until you figure out the social rythems. If you talk your head off, you'll learn when to back off. If you're quiet, you'll probably be perceived as insecure and never make any changes at all.
This is going to sound all new agey and ****, but I was talking with this buddist chick, and she was telling me about the 4 dimensions. Like imagine your life Completely free of worry, Imagine yourself being completely excellent with others,etc etc. ALl of a sudden I got this huge weight off my shoulders when I was imagining myself swooning all the people in bars and casinos and such. I saw myself as this awesome entertainer. Even doing the shyt for real had no where near the impact those visualizations had on me.
Then there is acting classes, comedy classes, making sure you have daily conversations with people, taking a job that provides interaction with strangers (sales jobs for example),etc. All of these things will get you better naturally, so you don't have to think like this anymore in the first place. If you took a sales job in the mall greeting customers that walk by, man, you'd never have to think what if some guy steals spotlight. You learn to interact with people so fvcking well, that would just almost never happen. You get so intune with people.