The biggest one that I've seen kill an interview is talking bad about your current/past employer. You went to work for them at one point and told them how great they were, right? Now your turning on them?

Always be positive. "They did X and I see that you do Y here. I really like that and I could really be a great employee helping you do Y."

Example - "The airline that I worked for dealt out information about delays different from yours and as a passenger/commuter, I liked the way you do it better and want to be part of this type of organization."

NEVER 'disrespect' your previous employer, even if pushed. Redirect the interviewer back on topic on 'why you want to work for them'!

NEVER say that you want to work for them for a pay raise. Clean kill!

Did I say be positive yet???

Also, like others have said, well dressed, paperwork in-order and be honest. An interviewer will be able to tell when your pumping up time and giving sketchy details about a time when...