[drinian]

Probably a bit late for most readers here, but I highly recommend taking advantage of whatever opportunities for public speaking and performance your high school offers -- whether that's just walking on stage as an extra in a school theater production, or joining the debate club. Even a little can go a long way in relieving anxiety for the rest of your life.

[aklemm]

Agreed. I participated quite casually all throughout high school, but it really taught me enough to be able to tackle any speaking opportunity with enthusiasm. And it wasn't even specific tactics that were important, rather it was all the experience.