Whether you’re preparing for a big interview, or your client is, or you need to train someone on how to be interviewed by the media, here are some tips to help make it as good as possible.
1) Always speak clearly and simply. Don’t use science or technology (or whatever field you’re in) jargon. Pretend like you’re explaining something to a third grader.
2) Find the time (if possible) to outline what points you want to say or answers to questions you anticipate. Write down everything you’d like to give in a response, then go back and edit it down to its simplest and shortest form.
3) We all goof up. If you realize you’ve accidentally said something incorrectly, offer correct information as soon as you realize what you’ve done. This isn’t as easy if you’re being interviewed live on television, so don’t lose your cool. But admitting you made a mistake is much better than letting the wrong information spread into public knowledge.
4) Never assume. If you’re being interviewed for an article, and you think the reporter has heard something incorrectly or you can sense there’s a misunderstanding of something, provide another, better explanation.
5) Follow-up is key. If you promise you’ll get back with the reporter with extra information, find out her/his deadline and get it there well before that.
6) It might sound like a no-brainer, but when you’re preparing for a television interview, know whether it’s going to air live or taped. Then enjoy feeling a little more at ease if it’s taped.
7) If you’re not accustomed to doing television or radio interviews, record yourself speaking so you know what thousands (millions?) of others are going to hear. If you’re happy with what you hear, that’s great. If you’re terrorized by the sound of your own voice, then work on it.
8) Speak simply and clearly. Again, record yourself practicing your answers, so you can determine if you need to slow down or speed up or enunciate. Nerves make us talk faster. (Avoid being over-caffeinated pre-interview!)
9) Know what your body does when you’re talking. Be aware of your gestures. Make sure they look natural. Don’t flail those arms.
10) Find out ahead of time, for a television interview, if you’ll be standing or sitting, inside or outside. Then dress and style accordingly. (No short skirts if you’re sitting; tie your hair back if you’re outside so you won’t be fidgeting with blowing hair while on camera; don’t wear white socks with sandals; don’t wear a shirt or skirt that’s too tight when you sit down.)
11) Make sure and ask where to look. Usually you look at the reporter, not the camera.
12) Be aware of your fidgets and don’t do them. (Playing with fingernails, biting inside of mouth, playing with your hair.)
13) For radio, know what type of format the program is: if it’s a hard news story, your interview will probably be brief and full of sound bites. For a talk-show format, you may need to fill 15-30 minutes with content. Make sure to be able to fill that time.
14) If you’re giving a radio interview by phone, stand up while talking! (Same works for phone job interviews.) It makes you more alert and helps your voice to carry clear and strong. Trust me, it’s obvious if you’re lying on the couch with your hand in a bag of Fritos.
abbymalikPR 
Lots of good points here Abby, but as someone who runs a lot of media training courses I think the key is that you really have to focus on what you actually want to get across. Otherwise your answers can be purely ‘reactive’ and you may get to the end of the interview and realise you haven’t said what you wanted to say, because they didn’t ask you the right question! Point 6 is an interesting one, on the merits of ‘live’ vs pre-recorded interviews. If you’re a beginner and very nervous, the latter is definitely best! But I always tell my clients that as you gain experience, you’ll probably enjoy the ‘live’ experience more – the extra adrenaline usually helps to sharpen up your performance, and you know that if you make your key points, they will actually be heard by the audience – they can’t be edited out afterwards.
Hi Tom: Thanks for the read and the comment! I think you’re so right: it’s imperative to make sure you focus on what you actually want to get across in an interview. This means knowing beforehand exactly what that focus is, and making sure your clients know that they’re allowed to steer the conversation back in that direction.