Forget your appearance. There was an anecdote back several years ago about a major computer company that would automatically not hire anyone who came to the interview in a suit and tie. People seemed to take that to heart to mean ALL companies thought that way and started just showing up to interviews in whatever was handy in the closet. This is a terrific way to give a horrible first impression. Compound it by not bathing or shaving, combing your hair, having bad breath, or wearing a lot of perfume/cologne and you are on the right track to not getting hired.
Don't communicate well. Either give long-winded answers that end up with you asking Now what was the question? or reply to the interviewer using one-word answers. Interviewers ask questions for several reasons - to find out how you think, what you think, if you can put logical thoughts together, if you can perform under pressure, or how creative you might be. Answers that are too long or too short are certain to derail your candidacy.
Don't think about your answers to questions before opening your mouth. Something stupid might emerge and the next thing you know, your foot is in there with your fillings. If you are interviewing for a receptionist position, make sure you mention you hate talking to people. If you are considering a banking position, don't forget to tell the interviewer that you have never balanced your checkbook - you just round up. These answers will really help make sure you don't get the job.
Do something stupid. Have an eleven o'clock interview? Bring your lunch along. The interviewer probably won't mind. Or even better, arrange to have a pizza delivered during the interview. The interviewer will probably appreciate the thoughtfulness. Chewing gum during the interview is also a nice touch. If you feel like you can't talk around it, you can always stick it behind your ear or toss it in the interviewer's waste can.
My personal favorite technique is stretching out on the floor and explaining that you think better while prone. That's always a winner.
Vent. Did you have a bad experience with your last supervisor? Was he a jerk? Be sure to regale the interviewer with all the gory details. I'm sure he will take copious notes. Don't forget to badmouth the company, too, because they expected you to pick up ten percent of your health insurance costs. What losers! The interviewer will really appreciate your candor. It will also help to name drop and be a know-it-all. Those are guaranteed to kill any chance you might have had for the job.
You are now prepared to go out and fail dismally at getting a new job. The best resume in the world won't help you once you put these actions into practice in face-to-face meetings with hiring managers. Go forth and bomb those interviews!