General behaviour: remember, you are being assessed at all times, possibly from when you enter the building and approach the receptionist, certainly from the moment you walk into the interview room to the moment you leave.
You must be as natural and relaxed, physically and mentally, as possible, but also professional, polite, and courteous. Never argue, unless you have been given a direct instruction to give your opposing views.
Be alert, show an interest in each interviewer as the ask questions, and answer directly to that person, but occasionally look at the others during your answer. In answering questions, don’t be evasive, be confident, and use your answers to demonstrate how you would make a good match for the position on offer.