Whether it's radio or TV, there are ways to make an interview work really well. Here are some of my top tips:
1) Stay calm and confident. Interviewers may appear intimidating, but they are simply professionals doing a job. If you work with them, the outcome will be good for both of you, so stay calm and express your views slowly and confidently.
2) Only say what you know. Speculating about a topic that you don't understand, or offering an explanation for events without any real evidence, are both routes to disaster. It's perfectly acceptable to admit that you don't know the answer to a question, but you will endeavour to find out. That also gives you another opportunity to be interviewed.
3) Keep still. Even if you are in a swivel chair, keep your feet on the floor and keep the chair still. Avoid nodding your head as the interviewer asks a question, since a reaction shot will suggest that you agree with the point they are making.
4) When you have made your point, stop. Interviewees can get themselves into terrible tangles if they try to keep speaking to "fill the dead air". Silence is not your problem, it's the interviewer's, so allow them to deal with it.
5) Leave edit points. Pause between the end of the question and your answer, and between your main points to allow the possibility of sound bites. It will greatly increase the chance of your words being re-broadcast.
6) Plan a memorable phrase. We're not all as witty as Oscar Wilde was (and he used to prepare his ad-libs too). Plan a memorable phrase well in advance, and as just mentioned, pause before and after you deliver it.
7) Leave your details behind. After the interview, make sure that you leave your contact details with the producer, the runner and the receptionist. They may call you back directly, or give your contact details to anyone who calls the station.