Be enterprising. As many topics as possible should be original rather than re- used from the usual sources. Dig for trends, people and events that are flying under the radar. Find events and issues that will have lasting impact on your listeners.
When using derivative content, ask how your treatment of the topic can advance/deepen it for your listeners. What new information and perspective can you add? Don’t settle for repeating what people have already said and your listeners have probably already heard.
Be focused. Narrow down the topic by creating a focus statement that clearly states what, why, who, and where. The ideal focus statement describes something that happened to somebody for a reason.