In the previous post somebody picked up on the point about radio presenters nodding when they interview you. It's remarkable what a key part of the broadcasting skill set nodding can be. In daily life they would you say "yes" or "uh huh". On the radio they have to use body language to do two things:
1. Get you talking.
2. Shut you up.
I have to turn off the Today Programme when I hear a "civilian" being interviewed because I know that by the time the interviewer has managed to get them talking it'll be time to shut them up, often with embarrassing abruptness.
Hence a fairly experienced hack like me knows that my main job is to start talking straightaway and keep going, while looking out for the tell-tale tics that indicate that the presenter either wants to move me on to another point or terminate the thing with something that could be passed off as an ending.
If it's a programme I'm used to doing, like "Front Row", they will tell me how long the item is and what illustrations they want me to cue. In such cases both the presenter and I are looking over each other's shoulders at the clocks behind us rather than at each other. If it's night time radio where you have generally been brought on to give the presenter a little thinking time, once they fling you a question you keep that answer going until it looks as if he's stopped taking instructions from the producer in their headphones and is ready to rejoin the conversation.
Of course none of this works if it's a phone interview. In that case you have to listen out for the strangulated vocal noises that indicates that they might want to cut in. Either that or the dead line that announces that they've already dropped your fader.