What you should do during the interview:

Give the interviewer a firm handshake, even if the interviewer is a woman and you are man. Nobody likes a limp handshake but by the same token do not take the person's hand off either. While shaking, introduce yourself, keeping eye contact at all times.

Nothing is worse than an interviewee who looks depressed or indifferent so smile. Would you want to work with someone who is always depressed?

You are confident about yourself and your capabilities then relay that. Do not stare out of the window or fiddle with your pencil. When the interviewer is talking to you, or you to him, be attentive.

Do not mumble your words as it portrays a lack of confidence.

If he makes a joke, smile to acknowledge that he made one, even if it was not funny.

Make sure you have understood the question if you do not, ask him to clarify it. Take a second, then answer.

Answer promptly and intelligently. However, when asked yes or no questions, elaborate and take it as an opportunity to sell yourself. 

Even if he does not ask you "Do you have any questions," ask him anyway and have these preplanned.

Be sure to thank the interviewer for his time.