Many authors and publishers dream of national TV interviews, and there's no doubt they are great. But they reach a mass audience, many of whom may have no interest in the topic. It's why book publicists will tell you that the niche audiences and longer-form interviews of radio and podcasts can be much more effective. Smaller audiences of highly interested listeners can add up to surprising book sales. If you've written a book and are promoting it, it's to your advantage to do well in podcast and radio interviews. Media trainers offer a range of suggestions, most of them easy, to improve performance.
At the start, record and listen to your voice to understand how you sound. Then answer some questions and listen to your replies. Are you enjoyable to listen to and easy to understand? If not, practice a few more times until you improve the way you sound. Even a modest improvement can make a difference when you're on the air. Keep an ear out for filler words (umm, like, you know what I mean?) and try to reduce your use of them. They serve no purpose and may make a poor impression on some listeners. Many media trainers also advise that you stand during the interview if it's happening by telephone.
Even though listeners can't see you, dress professionally. We tend to speak and act more professionally when dressed for the occasion. Then as you're moving from the basics to more nuanced things, keep a focus on the soft-sell approach. If you're going to make a direct mention of your book, wait for natural moments to do it and avoid saying it more than once or twice. Some hosts won't mention your book until the end of the interview, and don't worry if it happens. Your strategy is to use the discussion and your replies to questions to build credibility with the audience and seem knowledgeable and helpful.
It's wise to keep your answers to a reasonably short length to avoid confusing people or making them lose interest. There needs to be good pacing between you and the host that is conversational and enjoyable for listeners. On the other hand, don't be overly brief. Only in rare cases is yes or no with no follow-up a helpful answer. Make sure you have a glass of water nearby in case your mouth becomes dry from speaking. Always thank the host and off-air the producer at the conclusion. If you can get listeners involved through call-ins, you'll improve audience engagement if the show format allows for it.