Once you're satisfied . . .
You've practiced and/or rehearsed to where you feel you have the tunes down cold, and . . .
You're bass is solid and good to go, and you have extra cables, batteries, strings (maybe a backup bass as well), and your amp and cabinet and/or DI is good to go, and . . .
You were there early for soundcheck/setup, which went well, and . .
You're there early for the gig, dressed and feeling good, then . . .
Get out there and play it like you own it. It's fine to be nervous, but DON'T seem anything but cool as the other side of the pillow. Confidence is contagious, so you step up to the stage, play your part, and keep your head and ears on a swivel so you know right where you are and where everybody's going.
For those of us whose first rodeo was a long time ago, you simply prepare, perform, and have fun. It's a gas, gas, gas !
And remember:. EVERY bassist you admire or have listened to many times has done just you are about to. And forget stage fright, I've never had it. All those people out there are there to hear some great music and enjoy themselves. Roll with it.