1. Show up in professional attire. Although we've heard this rule a thousand time we still have people that choose to be unique and break this rule from time to time. OK a little more often! LISTEN college grads, be trendy on guys/girls night out not on your Monday morning interview!
NO!!!!!!!!!
YES!!!!!!!

2. Know your stuff! Do research on the company. Come prepared to ask intelligent questions about the company's products and or services. A lack of this basic knowledge such as goals of the company, and management information is a insult to the employer. This is also a double edged sword. You don't want to apply for a job that you aren't qualified for or really interested in. But if you want the job DO YOUR RESEARCH!
3.Language is also important. You don't want to come off like an air head. Don't use things that you would use in a text, orally or written on paper. For example, TTYL, LOL, profanity, etc. is not acceptable under any circumstances.
4. Just to piggyback off of language, facial expressions are also very important. Everyone loves a smiling face. I advise that you practice in the mirror a little bit everyday. Self control is extremely important. What if the interviewer does something totally embarrassing, is the interviewee suppose to burst out into laughter. I THINK NOT! Work on your poker face.

That's just my two cents on interviewing DO's and DO NOT's!!!