Visualize problems that may occur (What if I forget to say something important in my talk?) and plan how to deal with them. (E.g. Say, "When I was talking about XXX, I forgot to mention that...”
Use relaxation techniques
Tense and relax your hand muscles while waiting your turn.
Practice deep breathing while waiting.
Laugh; try to think of something funny.
Repeat a positive "mantra" or calming phrase to yourself.
Think positive thoughts
You know more about this topic than the other students in your class.
The audience likes you and wants you to succeed.
A speech is not a performance but an act of communication; focus on the message.
No one will notice that you are nervous (they can't hear your heart beating!)
It's normal to be nervous at the beginning of a speech; get through the first 30 seconds and you'll be fine.
Role play
You are a world famous expert speaking on your topic in a TedTalk.
You are a teacher giving a lecture.
You are only talking to your friends and know that you can impress them with.