Get to know the city. Even if you do not frequent your local Target, K-Mart, or Home Depot, you should at least know people who do. Eat where your listeners eat. Shop where they shop. Stay curious, alive, and interested.
Discuss show ideas with somebody else.
Prep is much easier when you have the luxury of working with a talented producer. He or she can help form questions you will ask on air and points you will make to engage your audience. Try bouncing the ideas off anyone around you - the call screener, the PD, someone in news, or the station's security guard. It may help you focus on what is interesting about the topic, or take it in a different direction. Testing out an idea should not be confused with rehearsing a monologue.