Deep breathing exercises may seem cheesy, but they really slow your heart rate, lower your blood pressure, and reduce your adrenaline flow. So try breathing in through your nose, holding your breath for five seconds, and breathing out through your mouth. Do this at least three times, but don't go over six, or you may either keel over or start to hyperventilate. If hand gestures are a part of your presentation, shake up your hands to get the blood going. This exercise will make it more natural for you to move them around during the performance.
Vocal exercises can help.
Prepare your mouth by running through your speech at full voice several times. If you screw up, just keep remembering that the audience won't have a text and see where you screw up. Just move on as if nothing happened. Even if you're not, the better you fake it, the more comfortable the audience will be with you, and thus, the more positive vibes they'll throw your way. This can be used to your advantage because if you make sure you walk onto the stage with a bright smile and confident posture, you already have it made.