You're sitting there with noone to talk to. You notice a group of aquaintances standing chatting to each other, and decide you'd like to go over and join in the conversation. Personally, I feel awkward about going over and just standing there with them in case I don't actually get the chance to speak for 2 minutes or more and they think I'm weird or something. But I can't really wait for someone to say something that I can respond to and then go over, because I'm usually not near enough to hear what they're saying. And standing near them, but not actually with them would probably look even weirder than standing with them and not contributing anything to the conversation for 2 or 3 minutes.
So how do you join a group conversation? Just stand with them and risk not getting a chance to say anything for the first 2 or 3 minutes, or what?