A new book by Lara Hogan includes some of my favorite advice about public speaking:
As you stand on the stage, remember: your audience is anticipating you'll be successful at giving this talk. To them, everything has been well thought-out and prepared; they walk in assuming (rightly!) they're going to learn something new or be inspired...and you're the person who'll show them how.
More, they want you to be successful and are quite forgiving. In my experience, you only lose them once you disrespect them (e.g. "Sorry if I'm not very prepared, I wrote this on the flight over here." annnnnd you've lost me.)
Hey while you're over at the A Book Apart store buying this, I heard this one is good.