Don't make derogatory remarks about fellow peers or former employers. Follow the rules of common courtesy throughout an interview. Shake the interviewer's hand when you leave. Make sure to thank the interviewer for the time spent and thank the secretary on the way out. A smile can be contagious and help calm your nerves.
Most people enjoy talking with someone who is smiling.
It is an indicator of good attitude and one that others will want to be around. After the interview, write a thank-you letter within three days to a week. Not only is it good manners, but it helps the interviewer keep you in mind. Briefly mention a specific event that will remind the interviewer of your conversation. Be sure to explain what you found interesting about the job and how your qualities would be of benefit in the position.