The CareerBuilder survey of hiring managers found that the most frequently mentioned mistake that job candidates make is dressing inappropriately for the interview. When applying for any kind of office job, men should wear a business suit and women a pantsuit or conservative skirt. For non-office jobs, that level of formality isn't necessary, but your attire should be neat and clean. When in doubt, always dress more conservatively than might be required. No jeans, sneakers or T-shirts, and it's generally best to skip cologne and perfume.
Arrive about fifteen minutes before the interview is scheduled, and stop at a restroom to check your appearance. Keep in mind that from the moment you walk in, you are creating an impression. Be courteous and professional at all times. If the interviewer invites you to lunch, pass on the alcohol -- you need to be as sharp as possible.
Bring a pen and a note pad. You should usually prepare a few extra copies of your résumé. Others involved in hiring may want to look over your credentials. You should also bring along any documents -- reports, graphs, project summaries -- that illustrate successful projects you've completed at other jobs.