A major problem for those who aren't practiced at public speaking is the anxiety evoked by standing up in front of people to talk. I know how debilitating this can be because I suffered from it myself when I first started teaching. Unfortunately, I don't know an easy way to overcome this anxiety. There aren't any magic words to make the fear go away. However, there are some things that can help.
1. Avoid drinking a lot of caffeinated beverages before you talk. Yes, you need to be alert, but fear will probably do that for you anyway. Caffeine is a stimulant. In some people, even low doses of caffeine can actually create anxiety and even trigger panic attacks, especially when taken in association with an already anxiety producing event. Almost everyone who takes high doses of caffeine will increase their anxiety levels. Don't make yourself more nervous.
2. It's less anxiety provoking to talk about facts than opinions. Part of a speaker's anxiety will be the fear of being wrong, of making a mistake. Facts can be memorized and one can site supporting documents for them. That makes them hard to argue with. Opinions are easy to argue with. Everyone's got one. So, make as much of your talk factual as possible.
3. Practice, practice, practice. The more you prepare, the more you can knock your presentation out while half asleep, the less anxiety you'll feel.
4. It's good speaking practice to make eye contact with the entire group that you're talking to. However, early in your speaking career, you may need to find one or two supportive people to keep looking back to. You know, the folks who smile encouragingly when you make eye contact. If possible, why not salt your audience with a person or two who will offer such support and encouragement. I know that I like to have a few friends in the audience when I talk, although it's not always possible to do so.
5. Prioritize your presentation. People who teach you how to speak will tell you many things that you should do. Trying to remember all those different things can be intimidating. Keep in mind that your actual "talk" is priority number 1. You need to speak clearly and loud enough to be heard so that your information will be conveyed. A second priority is making a connection with the audience through eye contact, gestures, and smiles. Whether you have good posture or not, or whether you stand still at the podium, are lower level priorities. Don't let worry about those issues interfere with the more important elements.
6. Deep breaths and relaxation before you talk. Do things that normally help you combat anxiety.
7. Time passers. If you need a moment to think, a moment to remember where you are in your talk, have a glass of water handy to sip from. The audience will give you the time you need. Just don't stand there and hem and haw
8. Finally, if all else fails remember that it'll be over soon, that you'll still be alive, that the sun will rise, the earth will turn, and somebody somewhere thinks you're OK.