I suggest about 4 oz of Gatorade about 15 mins before performance. (The dosage may vary with individual sweatiness.) I found that stage fright often causes a drop in blood pressure and that sipping a little Gatorade (or eating a small melon slice) does wonders. (Don't drink so much that the bladder becomes a problem.)
Other tricks (psychological) are to imagine that the audience is dressed in their underwear or that they are just cantelopes or sheep. I like to think that the audience is there to hear me and thus I'll give them something worthwhile (a big ego helps.)
In extreme cases of stage fright, this wouldn't work (Gatorade). Also, there is an INCREASE in blood pressure with the Fight or Flight response (i.e. stage fright), not a decrease. The mental imagery trick would be beneficial in a person with a more mild case of stage fright.
I'm in a band. The surefire way to kill stagefright is lots of practice, 2 or 3 vodka and tonics about 15 minutes before you hit the stage, and a flask full of whiskey. I've also heard that smoking a big fat joint with your bandmates helps, but that's illegal and of course I would never engage in such activities.
:-O
Your mileage may vary!