Be prepared. If you are in the position to rehearse what you say, do so. If you don't know the answer to something, take a breath to think about what you say before you say it. Don't look into people's eyes, but look at the tops of their heads. Use a little body language/flip charts/pictures to divert the audience attention from you. Enjoy what you are saying and believe in yourself for others to believe in you. I've spent quite a bit of time on stage (acting, concerts etc), but I still get a little nervous every now and then when holding a meeting at work. It's natural.