The big guys, of course are the BBC and crucial to remember here is that the BBC is not allowed to advertise. However, they'll often ask when your book is out and where it's available. The other trick is to find ways of talking about your book in such a way that it isn't advertising it. You might talk about how you came to write the book, whether it has a local connection or whether it deals with a topical subject.
It's often easier to get radio coverage for non-fiction rather than fiction though if you've had to do research for fiction there may be an angle you can find there.
Usually, the programme editor will discuss with you before the recording what s/he will ask in the interview. Sometimes they will do this well in advance, other times it will be just before the you go on air.
Being everywhere at once
Very often these days the interview will be conducted by phone so you can work form the comfort of your own home. It's an idea though to dress as if you were going to work – and this can mean casual for a writer - but don't stay in your pyjamas. It might also be an idea to stand or sit at your desk. This immediately makes you more business-like.
Sometimes also you may be called into your local studio to be connected to another. For instance, I was interviewed for Radio Leicester in the studio at Bangor, North Wales.
How to find who does what
The radio Times is your best friend here: http://www.radiotimes.com/radio/radio-listings/ Dip into it now and then to see who does what sort of programme. Ascertain the name of the producer before you approach them. Carry on building that database of contacts. (See previous posts) Your press release is important here again but do cover it with a personal note. Make it clear why they should be interested in interviewing you.
Preparing for the interview
If you've had a lot of warning, you can get a friend to play the part of the interviewer. Record your interview. It's a little shocking if you've not heard yourself before, but get used to it now. Does your voice need softening or lowering a tone? Don't go as far as Maggie Thatcher did, though. Are you humming and ahing a bit too much? Are any of your answers inadequate or too defensive?
If you don't know what you'll be asked far in advance, listen to a few interviews and use some of those questions.
Nurse your voice. No dairy just before the interview. Gargling with red wine is supposed to be good.
A few nerves are productive – they keep you on your toes – but you shouldn't be petrified. Take a few deep calming breaths before you start.
Then just enjoy.
Other than the BBC
There are other companies who do spoken word radio broadcasts but they are more difficult to find and won't give you as much coverage as the BBC. They may nevertheless be worth pursuing if you enjoy talking to other people about your work.
Doing your own thing
You can of course simply make your own podcast. Load it up to You Tube. Embed it in all of your sites. Again, take your cues form radio interviews you've enjoyed.