For me, its practice, practice, practice. By the time I'm done practicing, I have everything down, from how I'm going to pronounce each word to hand gestures. I know which words I'm going to emphasize, where I'm going to pause, all that stuff. And for some reason, I always feel better when I'm holding something in my hand. So I will hold a pen in my hand like I'm going to write something if I need to during the speech. No one notices.
And if I notice that my voice sounds shaky as I start out, I will speak louder. That will usually clear that up.
And also keep in mind, what would you be doing if you were in the audience, instead of doing the speech? Some people may be doodling, or may be lost in their own thoughts, others may be nodding off, while others may be watching the clock because they have big plans for the evening. Point is, they are NOT all sitting there transfixed on you, critiquing your every move. This assumption is what makes many people get nervous, I think.
And remember, giving a good speech isn't something to be embarrassed about. Getting up there, speaking clearly, and making eye contact is something that most people will look at with envy.
Its when you get up there, not wanting to try because you are afraid to look foolish, is when you actually look foolish. Starting to giggle, rolling your eyes because you don't want to be there, sighing because you don't want to be there, clowning around because you don't want to be there, I've seen all these things. If your in a speech class and see people doing this stuff what goes through everyone's minds? Something like, "Just hurry up and get on with it!"
And if you have some attractive females in the crowd, thats an extra boost. It gives you more push to do a great job. Its a lot more impressive to get up there and give a good performance, than to get up there and fumble around. You exhume self-confidence, and people notice it, even if you did fake it.