Well I would say make the person you're interviewing comfortable with a down to earth introduction before jumping into questions.. Offer a drink and re-assure them to take take their time with answering questions... Also choose your questions wisely which are relevant to helping you find the right person... Also avoid talking about yourself and give the person a chance to talk about themselves... after all the interview is about them and not you ;-)
You'd be surprised at what the microphone picks up. Dry mouth sounds is, unfortunately, one of them. Since no one wants to hear a sticky mouth interview, drink lots of water -- even during the interview!! :-o
Make sure that you're confident but not too much. You have to make the interview light, but make sure you still have a sense of authority. In our workplace, some of us are given the chance to hold the interview, it's not because we want them to experience what we experienced, it's because it helps us understand what its like to be on the other side (previously I was the one who was being interviewed, now I'm the one who holds the interview)
I think in order for you to be at least confident before your interview, you need to prepare yourself. It's always best to know the background of the company's profile. Anticipate questions from the interviewer. You don't need to answer all even you don't know, but you would give an impression that you understand what you are talking about which is a plus factor. Allow to be your best self no matter how intimidating the interviewer is. Sometimes it's not what you say, but how you say it. I hope this helps