That's a good point. Most of the time the audience don't know what you'll say, so you can afford to forget minor details or make sh*t up on the fly. They'll be none the wiser.

In public speaking, I find that things go a lot better if you're enthusiastical about the subject of your presentation.

Unfortunately, you can't always pick a topic you enjoy, but it's possible to convince yourself and the audience that you just love to talk about whatever you've to talk about, and that you are simply amazed by all the wonderous aspects and discoveries and figures you've encountered.
It's rather like presenting a homeshopping programme really, though you don't want to go over the top to an extent that it's not believable and you're sooner performing a sketch than speaking.

In my experience, it helps distract you from the big scary audience itself, it helps keep you from droning on and on at the same tone, from reading your sheets aloud and it'll help engage the audience because they'll share in some of your energy and enthusiasm.
It's really just one technique to help you forget, for the duration of your presentation, that you are no good at public speaking.

Confidence = relaxation.

Most of the tips here are really good. It's especially important to breathe normally, slow down, and try to relax your throat (tenseness is what makes your voice go funny). If your speech is any length at all, take water with you to the podium; it offers you the chance to take a breath, break eye contact, and relax a little.

Know your subject, and if you are working from a prepared text or notes, practice a few times at home. Focus on the mechanics of your speech, not the context in which you are giving it: the keys are breathing, tone, volume, pacing, and eye contact (it at least keeps you from looking down the entire time).