Candidates don't do their homework. Before you meet with a company, check out their web site, ask for a copy of their annual report, go to the library, and remember to ask the recruiter for any information they may be able to provide. This accomplishes a number of things. It flatters them that you have taken the time to do the research and shows them that you have a genuine interest in their opportunity. It can also either answer questions that you might have had, or bring up topics that you can discuss in the interview.
Candidates forget to interview the interviewer.
Don't be hesitant to ask questions about the interviewers themselves. Feel free to ask the interviewer about what brought them to the company and what keeps them there, what their expectations of you are and what your role will be within the company. This is your opportunity to do some fact finding. Some interviewers want the bottom line business-wise while others want to know a little more about you as a person. Keep your answers simple and to the point.