First of all, focus on the audience you are going to talk to. What are their interests, needs, concerns, fears at this point in time? If you have some of these answered you will have a starting point.
Secondly, think about your knowledge, expertise, and areas of interest. Think about how it can be made relevant to the audience you are going to talk to.
Thirdly, think about recent happenings. What are things that are being talked about in the world or in your locality? What or who is making news headlines at this time? It can be in the world of politics, entertainment, sports and games or even climate change.