Be on time. There is no excuse for it, none! Leave extra early, do whatever it takes. Blaming it on traffic or anything else doesn't matter (even if it is true).
Dress in a clean and conservative manner. Always wear professional attire to the interview, even if you have heard they are "business casual".
Turn your cell phone off. Double check that cell phone ringer is turned off.
Do not chew gum or have candy in your mouth.
If offered coffee or soda, "No Thank You" is the appropriate response.
If there are magazines or newspapers in the lobby - leave them alone! Be alert and ready.
Your purse should be on your arm and your briefcase should be on the floor, so you can be ready to stand up and extend your hand as soon as the hiring authority comes to get you.
Take multiple copies of your resume. You never know when you might be asked to meet additional people. It shows that you are prepared and serious about getting the job.
Take a reference sheet, not reference letters. Provide the reference sheet only if you are asked.
Don't badmouth a previous employer, ever. Perhaps they were a bad boss, but expressing that is a huge mistake.
Know the company and why you want to work there - Google the company you are interviewing with and learn as much as you can.
At the end of the interview, make sure you have some questions to ask. This will reinforce that you have a strong interest in the job.
Ask for the business card of each person you meet. This way you will have all of the information you need to write "thank you" notes. Email thank yous are acceptable, but be sure to proof carefully before hitting the send button.
Our job is to get you in the door. Your job is to "get the job". Go into every interview with the goal of getting an offer. Be enthusiastic, upbeat, and positive. Show your interest. Do not leave any doubt in the minds of the people you interview with that you are interested.