The biggest advice to a speaker giving a fixed speech is: PRACTICE!

People never put in enough practice on a speech. When I build a new speech, I practice it with a clock and record myself. And then edit the speech. And then deliver the speech again. And do it again. And again. And again.

By the time I'm done, you can take my slides, destroy my computer, put the room in a war zone, and I can still deliver that speech cold and make it at least passably interesting to the audience.

Yes, making a good speech is a ton of work. I don't do it often, and when I do I try to make sure I can give that speech multiple times to amortize some of the work.