While you are standing in the wings, waiting to go up in the limelight, do not feel that the audience is an unknown quantity, waiting eagerly to jump upon you, to greedily point out your mistakes and make fun of your every little stutter. The audience is as human as you are, and they really aren't all that bloodthirsty. Unless of course you are thinking about that undead audience in Interview with a Vampire.
It is the darkness and the silence that gets you most often the darkness of the pits, where the unseen audience sits, staring up at you, and the silence of everything else except your own voice, the awareness that you are at the center of attraction, and that everyone is marking your every word carefully. It seems one of the few places where that primordial fear of human beings the fear of darkness can still be seen in this age of electricity and atomic power is in the phenomenon called stage fright.
So the first thing to do on your way to becoming a successful public speaker is to address the problem of the silence and the darkness. Do not be intimidated by them. Learn how to deal with them, and your nervousness will disappear. You shall still have to learn how to speak well in order to actually be an attractive speech-maker, but well, it's a good beginning!
The commonest mistake that speakers make when they are on the podium is to address an empty space just above the audience's heads, the back wall of the hall or the distant horizon perhaps, presumably looking for an escape avenue. Do not give the audience a feeling that you are not involved with them. Impersonality is the quickest way to kill their interest in what you are saying. Rather, select a specific spot in the darkness, imagine a face there and talk to it. And shift your glance every now and then, to stare at another spot where another imaginary face is floating in the darkness.
Think of people with whom you have spoken all your life, and with whom you feel completely at home. Imagine their faces in the darkness, and speak as you would to them. This shall soon take care of the darkness for you, for it is not by speaking too formally or officially that you shall engage your audience, but by being direct and personal to them. When you look another person in the eye, they find it very hard not pay attention to what you're saying. This works for public speaking too. When you fix your stare upon points in the dark, your audience shall soon find themselves attracted to what you're saying provided, of course, that you aren't giving them drivel.
And the silence, too, you shall find out if you pay enough attention, isn't complete silence. There is no one out there waiting eagerly for you to put your foot in your mouth, so that they can jump on you and finish you. The audience, too, is merely human, just like you, and they too cough, sneeze, clear their throats, whisper to each other about important stuff, scratch their legs, yawn, and I regret to say even break wind. Just like you do. And if you listen carefully enough while you're standing in the wings, ready to go up, you can hear all these things, and you shall then realize that they are merely human, not monsters waiting to gobble you up. And then when you go up to the lectern, you'll find that your stage fright has disappeared.