I have been a presentation coach since 1980, so here’s my advice based on research and my own experience.
First of all, the more you avoid speaking the worse your aversion will become. To minimize the anxiety of speaking (glossophobia) rehearse under performance-like pressure and give yourself one-word instruction. According to Scientific American http://bit.ly/HcvT2V there are only two proven techniques to conquer stage-fright.
But even if you are fearless, you still need to learn the principles and practices of a 2000 year-old tradition: the art of rhetoric as passed down to us by Aristotle, Quintilian, and Cicero, among others.
1. You need to establish yourself as a trustworthy source of information.
2. You need to define the problem that your information solves.
3. You need to make the case for the importance of your topic.
4. Your ideas must be in marching order, preferably in the form of a story, and you must illustrate your points with vivid examples.
5. At the end, you must remind your listeners of what’s at stake, summarize your key points, and call them to action.
And what about your delivery skills? Here is Cicero around 50BC.
"One needs to read others’ motives to the very depths of human nature, since tickling or soothing anxieties is the test a speaker’s impact and technique. And do I have to mention the delivery itself—how the body is controlled, its gestures, facial expressions, vocal inflections and modulations. Unless this stands guard over the material, the material will evaporate, no matter how precious it was in itself."
The best way to overcome the challenge of public speaking is to just do it, over and over. Sorry to sound like a sneaker commercial, but it’s the truth. The Japanese say, “Fall down seven times, get up eight.” Which is another way of saying it takes 10,000 hours to make a good surgeon, a good lawyer, a good ballerina, and yes—a good public speaker.