First of all, you should bear in mind that you don't have to be brilliant or perfect to succeed in public speaking. Many of us have observed public speakers and thought to ourselves "Wow, I could never be that smart, calm, witty, entertaining, polished... or whatever." Well, I've got news for you. You don't have to be brilliant, witty, or perfect to succeed. That is not what public speaking is all about. I know it may look that way, but it's not. You can be average. You can be below average. You can make mistakes, get tongue-tied, or forget whole segments of your talk. You can even tell no jokes at all and still be successful. It all depends on how you and your audience define "success". Believe me, your audience doesn't expect perfection. I used to think most audiences did, but I was wrong.