I am an author and the host of a radio program about gardening. As the host of GardenLine I get sent lots of review copies of plant and gardening books, and I am happy to have many of these authors on the air to promote their books. Based on my experience I'm offering you folks some ideas for promoting your books on the radio.
1. Don't wait for them to find you. Send a review copy and a compelling note to every radio talk-show host in your region. Do your homework, of course. Don't send a novel to a gardening show unless it has a horticultural hook. Don't send a memoir to a program about finances and investing. Follow up two or three weeks later with an email if you haven't heard back.
2. Never just send the hosts an email press release - we all get dozens of these. Never put your press release in an attachment - we don't open them.
3. If you get a response and will be interviewed on the air, send the host or producer an advance thank you letter that has the following information: How to pronounce your name. Three of the most interesting things about your book. A "little known" fun fact about the book or the back-story of how it came to be written or published. Three sentences to use as your introduction. (Note: most authors don't do all of this because they don't want to be presumptuous. You aren't. You are making the host or producer's job easier.)
4. In your letter ask the host/producer who is their average listener. When you get a response, tailor what you'll say to that audience. Think of who that audience is and what their problems are or what they care about. Then find the ways that your book fits with those concerns/interests. Think of this radio appearance as your chance to make a personal connection with hundreds to thousands of people - don't leave that opportunity to chance!
5. Think about offering a special deal or contest on your blog or website as part of this radio interview. Give the audience a reason beyond your book to check you out on line! Offer them a discount, for example, if they use the radio program's name in their order. Offer signed copies to the listeners of the program. Make a special page of inside information that only they can see, including, of course, a link to ordering the book at the bottom of that page. Make that audience feel special and more connected to you than anyone else is.
6. In advance of the interview be sure the radio host has one or more copies of your book to give away. They can use it to generate calls or hits on their website/blog, and this gives them the excuse/reason to repeat the name of your book in other times once your interview is over. This is the cheapest radio time you can buy.
What's astonishing to me is that most people don't do the above. Most authors leave their interview totally to chance and don't do anything to capitalize on their radio time. Don't be one of those authors. When opportunity knocks, don't be the person who says "Can somebody else get that?"