Be well prepared...
Get to the show early for setup (so you're not rushing).
Allow yourself to have fun and enjoy the process.
Once the music starts, you'll get lost "in the moment"... and the nerves will subside.
Some "butterflies" before hitting the stage is completely normal.
On higher-profile gigs, it's also normal to feel a little pressure to "deliver".
The best thing you can do is get on stage, hit the big E chord, and start the show.