A well-known TV newsman once told me that everyone gets the butterflies. So show them how to fly in formation. Harness your nervous energy and transform it into positive energy. And no, imagining the audience in their underwear doesn't work.
Here are the steps I take to avoid getting weak-kneed:
1. Practice out loud. Repeatedly. Yes, I can hear you saying it's impossible to find time in your schedule to do this, but simple out-loud practice is the best way to calm your nerves. Go into a room and shut the door. Stand and deliver the presentation with passion. If you do this several times, the information will become second nature to you, and you won't suffer from the anxiety that comes with not being quite sure where you're headed.
2. Have them at hello with a powerful opening. If you've got a great opening that you know will move your audience -- a story, a visual, an unexpected prop -- it will boost your self-confidence. Also, you don't want to memorize the rest of your presentation -- that can be problematic if you lose your place -- but memorizing the opening is important. Again, the feeling of certainty will boost your confidence.
3. Breathe. I make a habit of the following breathing exercise: Inhale to a count of five. Exhale to a count of 10. Do 15 reps of this and it will have a calming effect. Going to the gym before your presentation works the same way.
4. Visualize. Do as pro athletes do. Play a little movie in your brain of yourself succeeding at the task you're about to perform. If you're at the foul line in the NBA finals, you would envision the ball going nothing-but-net before you take the shot. If you're about to be introduced before your speech at a conference, close your eyes for a moment and imagine yourself striding onto the stage with confidence and delivering a performance that makes you and your agenda look good. In a sense, you've "already been there" once you do this, and thus the fear of the unknown is minimized.
5. They like you. They really like you. Remember that, in most situations, the audience wants you to succeed. It's boring and awkward to watch someone dying up there on the stage, so draw strength from the knowledge that the audience is genuinely hoping that you'll entertain and inform. And if you happen to spot audience members who are yawning, rolling their eyes, or texting, to heck with 'em. Make eye contact with someone who's smiling or nodding her head in agreement. Instant confidence booster.
A few lucky extroverts out there don't have a problem with this. But for most of us, successfully dealing with stage fright is a learned skill, like correctly holding a nine-iron. And since public speaking is such a big part of career success, it's worth your while to slay the demon properly.