Know that you're not alone. Most people have some sort of speech anxiety.
If at all possible, stick to what you know and prepare well. It's easier to talk about something that you're comfortable and familiar with.
Know who you're talking to. Make an effort to talk to the people in your class (or whatever situation you'll be speaking in) and get to know them. This can make you more comfortable when it's your turn to speak.
Know where your speech will take place. If you've never been there before, go early and get a feel for it. It's easier to control your speech anxiety when you're comfortable in your environment.
Keep yourself in a positive mood. Don't think that you're going to do badly.
Always practice before a speech. The more you practice, the easier it will be to do again later. Try practicing in front of new people and asking how you can improve your content or delivery.
Ask a professor, minister, or more experienced friends for advice. It is a lot easier to get tips from those that have been through this before.
Volunteer to go first. The less time you have to think about your speech, the less nervous you'll be.