Rehearsal works great for fighting nervousness. Just the mere thought of speaking in front of 30+ people makes my heart slightly faster, but once I have a presentation down to the minute and can go through it 100% without looking at my notes, the nervousness dies down a lot and confidence starts taking over instead.
Of course, it reverses back the second you take a step into the stage, but it gets a whole lot worse when you don't remember what to say, and once you've spoken for 4-5 minutes the confidence seemingly remembers to come back by itself too.