Gee, the last time I applied for a job was 1974, but I've interviewed thousands of applicants since then (sometimes I was hiring an employee, and more often I was investigating the person for a security clearance or for a sensitive job in another government agency). I was pretty free to do whatever I wanted in the interview, and what I wanted to do is just chat and get to know the subject. Some people were very defensive, and seemed to be afraid to let me get to know them. Some tried to be aggressive, to take charge of the interview and get me to do what they wanted me to do. Some seemed downright dishonest and elusive, and I wrote them off right away - but I had to toy with them a while to catch them in lies I could document.
I looked for honesty, above all else. I also tended to favor people who had a genuine interest in the work, and in working in general. Intelligence, maturity, and common sense all help a lot. Knowledge of the job can help, but a person who's trainable is often more valuable that a person who got set in his ways at another employer.
I found it very difficult to hire people when I didn't like them, even if they seemed to be qualified for the job. I did hire a few, and I lived to regret it. So, it's a good idea to be nice, and to be human.
Good luck.
-Joe Offer-