Learn how to ad-lib. This is not performance art, this is an entertaining talk about the relevant business issue that you have been asked to speak on.
1) Have a large set of ad hoc examples, drawings, stories and anecdotes that you can draw on.
2) Have a broad understanding of a lot of subjects, both current and issue specific.
3) Be confident. They want to hear you, you have done this many times.
4) Be in the moment. (A bit more existential.) You need to be able to understand the "mood" of the crowd. Are you leading them, are you pushing against them, are they receptive, what are their concerns? And so on... this is a developed skill - not a taught thing.
5) Don't use visuals like power point, that is for longer talks, seminars or courses.
6) Have a contrary point of view to the conventional wisdom on the subject.
7) Get an understanding of stories, how they are structured and how to use them to get a valid point across.
8) Preparation is key. Get your facts in order, get your reasoning lined up. Test it, challenge it, try it out on colleagues and deliver it with the confidence that you cannot be challenged.
9) Take questions confidently. If you don't know, or it is something you cannot comment on, so be it. They understand, but do not duck the hard questions and do not be worried about giving a tough answer.
10) Smile... this is supposed to be fun, the world is not going to spin on its end because of your speech - so lighten up and enjoy it.