Im sure someone said this, but TALK OUT LOUD TO YOURSELF IN THE MIRROR! I know, I thought it sounded funny too, but when we had public speaking I realized if I can talk comftably to myself (out loud about the topic and got it all strait in my head) then it is ok. Also, before you go up, (the old-fashion method) take deep breaths, clentch your fists and relax (my teachers remedy).
GOOD LUCK!!!!!!!