Do not let the interview turn into an interrogation. Keep the interview on a conversational level. Start by thanking the interviewer for giving you the opportunity to see them. Begin by asking good questions like: How long have you been with the company? What firm were you with before you got to this company?
Make sure your interviewer can answer all your questions. Do not try to stump them.
Avoid talking about compensation during the first interview. Wait for the interviewer to bring up the subject. The interviewer does not expect you to take a position that is significantly under your past compensation level. If you did, you would quickly be looking for another position and the interviewer would have to do more interviews.
Be positive. Do not paint a negative picture of your current employer or past employer. If you do, you will be viewed as a complainer or management problem.
If the position does not match your skills, be sure to ask the interviewer if there are any other positions within the firm that would fit your talents.