To make a positive first impression, you need to know something about your potential employer, be well organized and well prepared. The object of the interview is for the employer to promote the company while you promote yourself.
Familiarize yourself with the job description so that you can leverage your experience. You want to be able to confidently emphasize your previous skills and how those skills can be utilized. You may even want to prepare some questions for the interviewer – this shows that you are as equally interested in them as they are in you.
Learn about the company by taking a look at their website and any available brochures or articles. Take the time to find out something specific about the company (e.g. awards, programs, status within the community) that you can discuss with the interviewer to show any common interests between your experience/skills and the position within the company.