Delay an interview if you are not in good physical condition, even if you have an appointment. Lack of sleep the night before the interview may be as much of a disadvantage as an attack of appendicitis. A cup of coffee or tea a few minutes before the interview may pep you up a little. During the actual interview, keep relaxed, yet alert. Relaxing is easier if you hold something  familiar in your hand, such as the book or magazines you were reading during the waiting time.