I can't really offer anything more than a personal anecdotes, but here is what I usually do for when I try to grab attention of a group of my peers:

• If you are talking to several people gathered in circle, and it is my turn to say something important, I make a small step forward so that I physically place myself in the center of the group.
• When I am speaking, I try to mantain eye contact with all people gathered around, If I focus too much only on the person I am speaking to, everyone else turns their attention towards them as well.
• I rarely do it myself, as I suppose it is a technique more tailored for public speeches, but conservative use of hand gestures to signify what you are talking about, probably won't hurt.
• I probably sound like a self absorbed jerk writing this, but if I want the attention to focus on myself, and not my interlocutor I often use "me" language. Compare and contrast ["What you say about vegans is true, but you may conisder..." - now everybody looks at the person who said something about vegans] ["I think that I agree with what was said about vegans, but I also think..." - now everybody looks at me as I explain my position].

But those are all just little little tricks, when the surest way of attracting attention of the audience is simply to have something important and interesting to say.