A lot of self practice. Starting with those you are comfortable with. Most people are unaware that your fear is not really in front of those that don't know you. Fear normally takes place in front of those who you know the best. Why? They will be your best and worse critics.
The other thing to try is walking around some when you do speak, not to much to disturb your audience where their heads are shuffling from side to side. Just enough to calm your nerves. Find a focal point in your auidence in different locations, it can be the clock on the back wall, a different wall just the middle of it. This way, you will not be looking directly at the audience. However, it will appear as if you are.
From time to time, do an overlook over the audience, not enough to scare yourself, just enough to make you look as if you are engage in what you are speaking about. One of the best things that ever happened to me, was I was thrown in front of new employees to train them on products and services. As scared as I was, it turned out to be the best thing for me professionally and personally. It help bring out more of my personality.
If need be, find community events, such as old folks homes, day care centers, small college classes to speak on topics that you know about. This way, you can gradually become comfortable in your skin in front of any crowd. Best of luck.
Oh, and use your sense of humor. Everyone likes to laugh. Even in the most serious settings. It shows you are human.
Michelle W. Fordham