Show up early. The clock starts running if you’re there or not.
Bring your patience and things to pass the time away. You’ll be waiting on the drums the longest. They are just the hardest things to mic. So bring books, movies, games and stuff that will keep you occupied and in the studio so when it’s your turn, you can jump right in.
Have an understanding of where the local music stores are in case there is an emergency.
Bring survival food and drinks so you don’t have to leave to eat unless you REALLY want to leave.
Let the engineer/producer do their thing. Don’t pester them on how long it’s taking. Getting tones is a part of their craft that IS billable. The clock doesn’t start when the band starts recording. There are hours of work involved before you are ready for that.