SO i'm going into a studio...manners?

Sit down, shut up and try not to get in the way.

Help keep the studio tidy during the session. Simple things like putting mic's on stands and running xlr cables when micing the kit can help. The engineer will want to place his own mic's though. DONT question his mic choice "don't you want to use a i5 on the snare instead of the 57?" Make sure to wrap up cables properly.

You task is to make his session easier. If you do so he will ask for you to come back. Don't constantly ask him questions during the session, explaining things properly can take time. No doubt the engineer will answer any questions you have when you're helping to tidy up at the end of the day.