I'll give you three words of advice my recruiter gave me when I went on my last interview: "Don't fʉck up." [spoiler]I got the job. ;D[/spoiler]

Haven't been on one in years, but I used to try to defuse the situation by looking around the guys office and try to spark conversation about something the interviewer is interested in. The less formal the interview, the more comfortable I always was.

Actual advice, will probably be superfluous to OP or someone who's not an idiot, but just reinforcing it for the younger people here who are going to get a job eventually: Clean shave. Showered. Cut nails. Fresh breath. Not too much cologne. But also, don't smell like shit. Teeth smile. If you have shitty teeth, mouth smile. Appropriate clothes. Not too casual, but you also probably won't need to wear a tux, both extremes look bad on someone. Too casual=don't really care about the job, too formal= insecure trying to over-do oneself to make up for known negatives. Ironed clothes. Clean shoes. If you accessorize, keep it minimal and complimentary. Guys = Watch. Girls = earrings and necklace if necklace goes well with outfit. Nothing about your outfit should be ridiculously flashy. That light up tie you wear on Christmas can stay home. Give a firm, quick handshake. Don't break the interviews hand, and don't make it awkwardly long. Maintain eye contact with interviewer. Maintain good posture. Don't say "um" trying to think of an answer. Think of your response before you say it. Don't fidget with your hands too much or look out the window, the door, the time, or your feet. This will make it seem like you want to leave. Don't touch your face. This shows nervousness. Don't cross your arms. This looks like you have an objection to something the interviewer has said. Inquire about further career possibilities in the company. Even if you're getting a job at a fast food place. Inquire about hours and salary. The employer is going to want someone who isn't going to come to them bitching about something they should have already known. If something is funny, don't over laugh. Be calm, cool, and collected. Don't be nervous, be confident. Have the mindset that you're going to this interview to learn more about your future job, rather than going to it to find out if your going to get a job. If you have the experience/resume the employer is looking for and you do all these things, you should in good standing. My mom conducts all the interviews for a high-end restaurant, which while it isn't a Fortune 500 company, they are extremely particular about who they hire, so these are tips that she's taught me as someone who has to interview people on a regular basis.

Do not complain about the furniture.

Be yourself. And dress appropriately. Grooming counts.

When I had an interview coming up for an internship that was really important I applied to as many places as possible a couple months in advance. When places started calling in for interviews I used them as practice and asked at the end if there was anything I could work on and after 4-5 interviews the real thing was easy as hell.

At the end of the interview ask your interviewer if there's anything they don't like about your resume/if there's anything wrong with it.

I find interviewing the interviewer a very effective method.

Talk about meatballs