The Interview
During the interview try to come across as calm, confident and professional but enthusiastic. It is natural for you to feel nervous and the interviewer will be expecting this, but it is important for you to be able to keep these feelings in check and allow your ability and personality to shine.
Know your CV! It sounds obvious but the interviewer will go through your details with you and will want to know the reasons behind any decisions you have made. Answer positively and be prepared to talk about facts and figures, targets and achievements. Back up your answers with examples of your own experience. Don't lie, or exaggerate - chances are you will be found out! It is also important not to be defensive or negative. If you are uncomfortable with any aspect of your cv eg exam results, practice talking about them prior to the interview until you feel confident about answering questions on this area.
Think about the questions that are being asked and what the interviewer is aiming to discover about you. Try not to use 'crutch' words to fill gaps when you are nervous ('sort of, you know, like, um') and don't be afraid of silence. It is perfectly acceptable to think about a question before you answer.
Maintain eye contact throughout the interview and be careful not to fidget, or play with your pen. Don't take notes as this may impair your concentration.