Words are important. In a radio interview they are immensely important. In addition to words being important, when broadcasting whether streaming live or recorded a preliminary program overview is not a bad idea. Neither is scripting or providing your commentator with talking points.
There are five, main types of radio broadcast, which are typically recognized. It is a good idea to become aware of them as an author prior to interviewing, read more here: http://www.examiner.com/article/radio-interviews-the-author-s-role?cid=db_articles