Always start an interview for a job or even for college admission with a smile. Try to use phrases like It is a pleasure to meet you, but dont be humble and dont praise the interviewer too much. It is nice to say something like I admire your work and even to give a few specifics, but you will embarrass yourself if you start to praise all the accomplishments of the person in front of you.
Read the interviewer. You can be sure that he or she has more experience than you do, but this does not mean that you cant read a few signs. If the interviewer s formal, you will have to be the same. If the interviewer is less formal, and he starts to make jokes and to create a relaxed atmosphere, try to act the same. Relaxation is required for a formal interview also, but this does not mean that you can put your legs on the desk and to light up a cigarette.
Good manners say that you should wait to be asked to sit down, or to ask permission to do so. Some interviewers just forget about this, but you should not take it as if they dont like you. If the chair is situated far from the desk of the interviewer, try to get it closer without making any noise. This proves that you are interested, but make sure not to invade the personal space, or to stay in an angle from which you can see the monitor of the respective person.
Take care of your posture. If you dont know what to do with your hands, put it on your knees. This is a sign of education. Dont stay with your arms crossed at your chest, as this creates an invisible barrier in the way of communication. Even the most experienced interviewers are people, so they know that you are excited. However, too much excitement would be annoying.