Make sure the sound guy gives you some good monitor (including vocals). You may not be used to the different sound mix while playing on stage... that comfortable sound you are used to in the practice studio will go right out the window! If you have a bad monitor mix, it can sometimes feel like you are playing allll alllloooooone up there

If you have IEM all the better.
Wear ear protection - nobody's ears are invincible.
Prep all your gear early. Make sure everything is tuned up, have extra sticks, pack some spare parts, etc...
And I agree with john_bonham73... the adrenaline will be going. You will probably play louder, harder, faster than you need to. Relax, listen, and feel the whole band. Keep that time steady.
Don't get stupid and get drunk on (insert favorite tasty beverage here) before hitting the stage. One or two to calm the nerves is sometimes OK, but better safe than sorry. I for one cannot play after hitting that BUZZ level... but to each his own.
Have fun!
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Stand back! I have a COWBELL... and I am not afraid to use it.........
Saluda Cymbals - B20 never sounded so good...