Public Speaking Tip #1:No one expects you to know everything
When I started teaching college French at UT Austin, I was nervous. I was so nervous that I would spend hours planning out a 50-minute class, just to make sure that I wouldn't be tricked up by those pesky students who were, of course, out to get me.
Ever feel that way when you're stepping up to the podium--that the audience is the enemy, happily rooting for you to fail?
The truth is that your audience wants you to succeed. They want you to give a great talk. They want you to quickly recover from any stumbles in speech or technical difficulties that you may encounter. They want you to be witty, entertaining, informative and engaging. You don't need to worry about impressing them; they are already on your side. So stop seeing them as the enemy; even the most skeptical faces in the crowd are just begging to be won over.
One of the most valuable things I learned as a professor is that no one expects you to know everything. People can sniff-out made-up answers, so just be honest. If you aren't sure of an answer, say so. "Hmmm. That's an excellent question. We do have a client who uses X, but I'd like to research that and get back to you." And then, of course, do the research and contact the person. You'll be much more respected if you treat a tough question as an opportunity for professional development rather than a chance to pump yourself up with obfuscation.