Dress

When you are being interviewed for a job, you should dress in business attire – or at the very least, make sure your clothes are appropriate for a professional setting.
Clothes should be spot-free, well pressed, and properly mended (i.e. no missing buttons).
Wear a pair of shoes (not sneakers or sandals), and make sure your shoes are clean.
Avoid “fancy” dress fabrics (like satin or anything metallic) – keep it simple and professional.
Do not wear see-through clothing or super-short skirts!
Jewelry and make-up should be kept to a minimum, and perfume or cologne should be subtle or avoided altogether (since your interviewer might be allergic). Remember, less is more in a professional setting.
Avoid looking sexy in a work setting! It is inappropriate and also does not convey your strong qualifications for a job.

Hygiene

Make sure you (and your clothing) are clean, as well as looking (and smelling) good!

Make sure your nails are clean and trimmed, and that your hair is well groomed.
Be aware of your body odor and make sure you use deodorant.
If you want make sure you look ok, use the bathroom (don’t groom yourself in public).
It’s always a good idea to make sure your breath is fresh by using breath mints or chewing gum before your interview -- but you should NOT chew gum during the interview!

Punctuality

Be on time! If you are late, people will notice and it makes a bad first impression.

As a general rule it is good to arrive at least 5-10 minutes early for an interview.
If you are going some place for the first time, make sure you have clear directions, as well as a phone number you can call if you have trouble finding it.
It is a very good idea to do a trial run ahead of time to make sure you know how to get there and how long it will take for you to arrive on time.
Saying that you got stuck on a train is not an excuse, even if it did happen!

Positive Attitude

When it is time to meet the people who will be interviewing you, attitude is everything! You will want all of your actions to convey a sense that you are comfortable, confident, enthusiastic, friendly, and polite. Here are some tips to keep in mind:

Hand-Shake: A firm hand-shake is very important. It shows your enthusiasm as well as being present and aware during your meeting with someone. You should shake hands when you first meet your interviewer, and also when you say goodbye. Try to maintain eye contact and smile whenever you shake hands.
Eye Contact: Eye contact is very important. You need to make sure you look at the person or people with whom you are speaking. Do not look at the wall or the floor when speaking to someone, especially during an interview. During a group interview, make sure you speak to and make eye contact with everyone participating, not just the interviewer.
Body Language: Make sure you maintain good posture both seated and standing. Avoid nervous body language like shaking your leg while sitting, touching your face, biting your nails, licking your lips, fiddling with your fingers. Keep your body language open. Avoid crossing your arms or placing your hands on hips and always maintain eye contact.
Be Yourself: The most important thing you can do is to stay relaxed and let your personality shine through. The purpose of the interview is for potential employers to see who you are as a person, so you should do with you can to show off the “real you.” Honesty, integrity, and sincerity are key -- obviously, it is never OK to make things up to try and sound more impressive.

Other Tips

Bring extra copies of your resume, contact information for your references, and any other information you might need in order to complete a job application.
Be sure to do some research on the company or organization before your interview.
Be sure to turn off your cell phone or pager before the interview!
Be aware that you might be asked to interview with more than one person, either in a group or one at a time.
Have some answers prepared to questions that are likely to be asked (e.g., about your skills, interests, goals, why you want to work there, etc.)
Answer each question as clearly as possible, but keep your answers concise -- don’t ramble on or go off on tangents.
Make some time to practice your interview responses and get some feedback.
Have some questions prepared to ask your interviewer(s).
Be sure to say thank you to your interviewer(s).
Be sure to ask for a business card / contact information from your interviewer(s).
Be sure to send a Thank-You Letter (to each person who interviewed you) within one business day of your interview.