Don't downplay your characteristics and skills. This is your chance to make them see why they should choose you over someone else. Also, try to make conversation with your interviewer that's unrelated to work.
When it's time for you to ask questions, you should interview the interviewer. Ask stuff like what is the most challenging thing for the department/manager, or what type of employee do you think would best fit the current organizational sructure, or how do you see my skills fitting within the department. The one thing a lot of people forget is that after you ask questions, make sure you follow up with relevant feedback. Just keep the feed back short and sweet. Sometimes, interviewers answer a question, then there's an awkward silence. The feeling of "that's nice to know...good for you" happens
Always bring your resume to an interview. A lot of interviewers come unprepared, give them things to talk about. Also, makes you look like you're on top of things.
