Talk to the interviewer or even pretend you are talking with your best friend and let everyone else eavesdrop. Usually your fear is of the unknown. Make sure you have good notes and give the interviewer a list of questions that you want to talk about. Don't let the interviewer surprise you with questions you are not prepared to answer. See if you can observe someone else's interview and see how it goes with that person and what you can expect when it's your turn.
Some people think better moving around.
Even on radio. Don't use any words you don't use in your everyday life. Using big words doesn't impress anyone and most listeners and viewers will be able to tell you don't use them regularly. You will feel the most at ease in your standard work attire. For TV, depending on the circumstances, a more professional look may be necessary even if it's not your normal dress.