If it's a group interview you are attending and are sitting around the table with others, be diplomatic. Don't be the "know it all" and take up all the conversation, but on the other hand don't sit there and allow all the others to get away with the self promotion. If you are given a group task to complete or discuss, think it over carefully and include the others in your discussion (shows good teamwork).
I have been to many interviews where some idiot on the table thinks they know all the answers to all the questions and has to be the first one to get their point accross because they think they are right and no one else gets a word in. They may know all the answers but thats not the point of a group interview. It's to see how well you can achieve an outcome, right or wrong. The interviewers know that most people new to the industry wont know the correct solutions, they just want to see how well you perform in a group.
Also when in the waiting room, do chat to the other candidates but don't start bitching about other airline interviews, or anything for that matter. My first interview was like this and it turned out the lady doing the registrations had as much input about you as the interviewers. I didn't know it at the time but she was watching how we integrated with the others waiting, and after I got the job I asked her about her role. She WAS there to watch you and listen to you. Remember, as soon as you walk into the place your every move and conversation is tracked.