I find interviews terrifying too, so I know exactly how you feel! I only had one interview, at the school I applied to (and got into) ED, so I don’t exactly have a varied experience.
It does help to be friendly though. My interviewer was really friendly to me as soon as we met, and I felt like she was good at not putting me on the spot; unfortunately that’s not a factor that you can control though. Either way, definitely don’t try to sound too rehearsed. And if a topic comes up that you’re really enthusiastic about, don’t hesitate to show that enthusiasm!