Brainstorm these questions beforehand:

  1. What is the main reason the employer would want to hire you?
  2. What do you have to offer in terms of experience and personality?
  3. What are two hardcore accomplishments that back up your interest in the position?
  4. What are some answers to objections you anticipate from the employer?
  5. Why do you want to work for the company (research the company)?
Be sure you have all this information in your head and are ready to express it at the interview.
On the day of the interview, make sure you radiate confidence.
If the conversation veers off-topic, steer it back to the answers you have prepared and memorized so that the employer will have a positive, lasting impression of you in relation to the job.

Lastly, relax and be your kick-ass self.