Be respectful and considerate of your fellow interviewees... if the person next to you made a great point, and they ask you the same question, you can always refer to what the other interviewee said, show that you're being attentive to what others say. If other people are talking, LOOK at them, think about what they're saying.
Be in the moment. Among other things, it will lower your stress. Don't sit there plotting what you're going to say next, you know yourself and your application better than anyone else, relax.
Remember, they may be interviewing you, but you are also in a position to interview THEM... you have to find the place that is right for you. Don't forget that!!!
If they (the interviewers) seem like they aren't paying direct attention to you, or maybe don't like you, don't let it rattle you. During my OMM Block 2 exam today, (during a break) I admitted to Dr. B that I liked him a lot better now, and that we get along great, but that during the interview he really didn't like me, why? He laughed and said he liked me then too, and voted for me to be accepted, so there you go... and I think I'm a good judge of these things... I was wrong!! They have a lot on their minds, they've got a lot going on, just be yourself and don't try to read THEIR minds... instead, know your OWN mind.
Gunners and jerks in these group interviews get shot down fast... our class is extremely cohesive, supportive, and friendly... they're looking for people who are going to treat each other and their patients with compassion and genuine interest. There is no benefit to being competitive at this point, just be yourself and see if this particular shoe fits.
Be empowered by the fact that they CHOSE you to come and talk to them, they're honored that you came, and they're interested in you. If it works out, it will be a mutual decision. They do not hold all of the cards, you are making decisions about them too.
Breathe!

Best of Luck!!
Christine