One thing I really find that works is to tell the class. Have your notes on note cards, NOT paper (paper shakes along with your hands). When you get to the front, just tell people, "Hi, I'm going to be presenting on *whatever* today. Please bear with me, I'm REALLY nervous but I'm going to do my best." Usually, telling them will help you calm down because once they know, you don't have to be nervous about being nervous (did that make ANY sense!). Also, it tends to help the teacher be a little more lenient, because if s/he knows you are nervous but sees the work you put into your project, you might get extra marks for effort.