If you drive, you must arrive to the interview with a clean car. Period. Most all of my clients walk outside with you after the interview to say goodbye. Your automobile is an extension of you. The interior and exterior should be pristine, not just clean. A potential employer sees a dirty car as a reflection of how you maintain your own personal belongings. This gives the impression, and rightfully so, that you would not be very effective when caring for their possessions. Take the extra fifteen minutes and run through a local car wash and vacuum your car. This step could be the difference in you landing the job or not.