After you set up; stop, take a deep breath and slow your heart rate down.
For my last gig I had to rush to set up and I didn't calm down before my first song. Made a couple mistakes more on the keyboard than I'd like to in the beginning.
Another thing: if you're playing an instrument that is on a table (like a keyboard), take some time to get used to it's height. Play through some riffs of a song with the sound off or something, it definitely helps nail down the muscle memory aspect.
Good luck~<3