Try to relax. The first thing to do if you are overcome fear of speaking, - to shrink into a ball and become as unobtrusively as possible. This impulse will only exacerbate your anxiety, and every minute before a performance will bring you psychological discomfort. So relax all the muscles instead of straining them.
Take an open posture. Do not cross your arms and legs. First, it will allow blood to circulate better, and, secondly, will demonstrate to the audience your openness and confidence.
Your body realized that nothing terrible happens, try to breath. Most often it quickens when you're nervous. Take a deep breath, counting to four and then exhale sharply. Repeat this exercise 10 times.
If you feel your voice breaking from the excitement, before the speech, do voice exercises. Tell of his speech aloud, not revealing a mouth. At the same time try to make your speech was expressive, i.e. was heard up and down votes. This will relax the facial and neck muscles, and to cope with anxiety will be much easier.
Stop trembling at the knees, if any. One of the ways in which it can be done, is the mental direction of their attention to them. If this method fails, you can try to "trick" your brain. Look at their knees and make them shake. Most often, they stop doing it.
Write down the main ideas of his speech, if your anxiety is because you are afraid of forgetting part of his speech. At any time you will be able to look at a cheat sheet and return to the thread of the presentation. You can attach this piece to the folder that your audience doesn't suspect anything.