Just do it.
That's the basic point. I was scared of public speaking at one time. So I did theater in high school. After practicing the play numerous times, when I went on stage I was fine. Why? Because I was confident in my knowledge of what I had to do. The more you do public speaking, the better you get. You just gotta do it, and do it and do it again. The first time you might be terrible. You might forget what you're going to say and stammer. But you know what you do? You do it again. And again. And again. And you will get better at it.
Another trick is to just completely desensitize yourself. I was scared of rollercoasters for a while. So when my friends and I were going to a rollercoaster park, I wasn't sure what I should do. Eventually I just figured that I would go on the tallest and scariest ride first, the Powertower. Now this thing goes and shoots you 300 feet into the air, stops, and then let's you drop. On the way up, I was frickin scared. I was shaking and and saying all kinds of crazy stuff. And then I got to the top. And I was just waiting to drop. And I could see for miles out, and all those little people on the ground. It was scary. And then I dropped. And you know what? It was actually kind of fun. I had built up all that fear for really nothing. The ride was actually fun. So after that I went on all the other thrill rides, because I had seen that there was nothing to be afraid of, and that I could just enjoy myself. That's what you gotta do. You gotta realize that you're basically afraid of nothing. Your fear is largely irrational. And if you do public speaking for the first time, know that that is literal the worst it will get. After your first time it gets easier and easier. Nowadays, I very much enjoy public speaking.