With 25 years experience in management, I have been involved in more than 1000 interviews and I have witnessed the very best and well, you get the idea. I stopped counting after I hired my 500th person. You only get one chance to make a first impression so make sure you are prepared.
Things You Will Need
A cover letter
Access to the Internet
Be qualified! The first thing I would suggest is that you do not apply for a job that you are not qualified for. It may seem like a strange statement, but I have actually interviewed people that tried to pass as a chemist when in fact they had no knowledge of chemistry whatsoever.
Do your homework! Find out as much as you can about the job you are applying for and about the company or organization from which you are seeking employment. Make a list of questions about the company. In a small company you may be interviewed by the owner and/or founder of the company. The success of their company is usually a very personal thing. Show you are interested and that you really care. Make sure you know the names of all of the people that are conducting the interview.
Dress professionally! Gentlemen, wear a suit and tie. Ladies, wear a business suit. Look your best. Make sure you are well groomed. Again it may sound superficial but we don't buy poorly packaged products at the supermarket so why would you expect it to be any different when you are presenting yourself. I would caution against wearing cologne or perfume.
Bring everything to the interview! Bring multiple copies of your cover letter and resume. Bring your transcripts. Bring your diploma. Bring letters of reference. Transcripts, diplomas and letters of reference have to be verified but having them shows that you have nothing to hide. I have to admit that I have hired people on the spot and took their references at face value. At times the employer is very anxious to get a position filled so they will hire the first qualified applicant.
Know what every employer wants! There are three main things that every employer wants: 1) Competent employees. You can be the nicest person in the world but if you can't do the job it won't matter how well you interview. 2) Team players! You have to be able to work well with others. Amazing, but it is the same thing we were graded on in kindergarten "Plays well with others". 3) Proactive employees! My first employer would always say, "Bring me solutions, not problems". Problems do happen but the difference between a good employee and a great employee is someone that makes my job easier by trying to solve the problem or can propose a solution before it comes to my attention.
Be polite and professional! Manners matter. Make eye contact at all times. Be punctual. Arrive 20 minutes early, but don't enter the building until about 10 minutes prior to your interview. You might be thinking that this is just common sense and you are right but there are uncommon people out there. For example; I was interviewing a young woman for what was basically a dishwashing position. She did tell me, without being asked (mistake number one) that she was let go from her previous job because her boss was a jerk and he told her that she had an "attitude". I let her ramble on (mostly because I was in shock) for about five minutes about how she didn't have an attitude. I thanked her for coming in and told her that we would call her within 24 hours if we needed her services.
Practice! Practice! Practice! Great athletes, great orators, and great entertainers have one thing in common; they all rehearse or practice before they perform. Practice in front of a mirror. Practice with a friend or family. Make a list of questions or check some of the articles on here to find potential questions. The more you rehearse the more you will be able to relax and be yourself during the interview. Unless you are absolutely sure that you know where you are going I would even practice driving to your interview. I actually had a prospective employee call me from the corner to ask where the door was to get in. He was drenched when he arrived. Not a great start to an interview. He did get the job but that is a whole other story.
Be confident not arrogant! Managers do not want to baby-sit their employees. If you can do the job then just relax and be yourself. Don't be a "know it all".
Use your judgment but I think it is a nice touch to send a "Thank you" card after the interview. I always suggest that you ask if it is ok if you call about the position in a few days. Some employers do not want follow up calls.