what are some mistakes that people make on interviews

Being very nervous. It give a impression to the interviewer that you are not confident enough. Dressing inappropriately also set bad impression to them. I think the way you present yourself during a interview is very important.

a big one is not dressing appropriatly for the interview. I don't care if you are interveiwing for a job flipping burgers at McDonalds, you should arrive with a neat clean appearence, and NO JEANS please......i am not saying you need to show up in a suit....or even with a tie on for goodness sakes, but a nice clean dress shirt/blouse and a clean, non-wrinkled pair or pants or skirt. Obviously being on time is important as well as you said.

Talking Causually as if you are not proffessional at all...