Practice practice practice! The more familiar you are with your content the more confident you will be in what you have to say. Remember they are on your side - they aren't hoping you fail, they are hoping you succeed and give them information they don't know. Take a deep breath before you start, smile, and consciously slow down (we all speed up when we are nervous) Focus on a couple of points on the back wall, just above their heads, so you are not directly looking at anyone (unless you have a friend in tehaudience who will smile and give you the thumbs up!!) and make sure you address the whole room.