Accept the fact that any oral presentation is done because you have information they want or need - so they aren't there to harass, heckle, or make fun of you - they are there to hear what you have to share. It helps when you are comfortable and knowledgeable about the subject matter, but even if you don't think you are the 'master' of the information, just remind yourself that you know more than the rest of them and whatever you share will enlighten them.
One of the best things I've done is to avoid getting freaked out about being outnumbered - looking at the audience can be intimidating and overwhelming. Recall that it is just a one-way conversation of you speaking your knowledge to another person. Focus on a single person in the audience to start your speech, but every sentence or two, switch who your focus is on and speak to that next person. Your mouth continues the speech along whatever path it needs to journey, but you feel like you are explaining it to one person at a time. This also works to keep you from looking spaced out (staring into the back of the room) or overly nervous (focusing on a single person, or a spot on the floor). By changing your focus, you keep your audience engaged and attentive as each one may be the next person you look to speak to.
WHEN (not if) someone in the audience is more knowledgeable and tries to correct you or trap you - don't let it throw you off too much. As with all things in life, there will always be someone with more insight. Just pause, and ask that person to elaborate the point for you - let them speak the meat of the point being made, and you can correct them as necessary. OR if you don't want to have the speed bump in your presentation, simply ask them to hold comments and questions until the end - and that most questions should be answered by the time you've finished. That should shut them up and leave you controlling the arena as you need to do.
The biggest and most important thing to remember - it's not the end of the world. No matter what you say or do, it'll be over and life will go on - so don't worry about tripping and falling down, or stuttering, or losing your train of thought, or having your fly unzipped (I forgot that as best man at a wedding) - Life goes on! Just do your best with the time given to you and the knowledge you have to share...it'll be okay.