You can research a speech generally to get idas for theme, and then specifically once you know what it is you want to talk about. You can research on the internet and in libraries, and you can consult your treasure chest of ideas saved over years of clipping and tagging.
But never forget your human resources. You cannot interview a website or book for clarification. Humans can expand on an idea, give you more information, or give you that quirky perspective that just might give you the winning angle on a topic.
