New speakers tend to speak too quickly. It is almost a fear of silence. Good speakers use pauses to give the audience time to consume what has been said. It also punctuates and can add emphasis to the presentation. So breathe, pace your phrases, allow a pause between topics or chnages of direction or where you want to draw attention to what is about to be said.
Going back to the comment on jokes, if you are going to use them at all, be very careful. It is better to avoid a joke if you are not able to deliver it with confidence, wit and style. The alternative doesn't draw laughs and if you are nervous, the lack of audience reaction will only make you feel worse.
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