Imagine yourself speaking, your voice loud, clear, and assured. Most of the time your nervousness doesn't show at all. If you don't say anything about it, nobody will notice. Concentrate on the message, not the medium. Your nervousness will dissipate if you focus your attention away from your own anxieties and outwardly toward your message and your audience.
Experience builds confidence, which is a key to effective speaking.
Your anxieties will decrease after each speech that you give.