Several people have advised to cover up tattoos. I bring it up because I once interviewed a girl for an assistant's position, and when I asked her to tell me about herself, she told me about her tattoo on her stomach and how it represented her view of herself----she didn't get the job. I interview people fairly frequently. Giving interviews is boring, its not much fun. Everyone is a team player and the like. They all sound alike. Everyone is BS'ing you, and you know it. Much of what I look for is subtle and the subject doesnt even know what I'm noting. For instance, when I am walking them back to my office I'll ask if they found the building ok, or if it is still raining or something. Those that just mumble "yeah, no problem" already are at a disadvantage. Any negative is bad. A better answer would be "yes, I have a friend who lives close by so I knew the neighborhood".
DO NOT SUCK UP!!! We can spot that a mile away. Suckups are weasels that cant be trusted. I usually tell a really stupid joke. If they laugh like its the best thing they've ever heard, they fail. If they politely chuckle and segue into something else, they are still in contention.
Above all, I am looking for someone who CARES. Someone who puts themself into their job, and it MEANS something to do it well, not just a way to get paid. And if you are female interviewing with a male, DO NOT under any circumstances flirt or use your looks to try to influence the interviewer. All that says to me is "potential sexual harrassment problem".