Remember: You're a pilot, it's an airplane, flying in the system. When you're the PF, take charge and be a pilot.
Visuals are probably the hardest thing to do well as a new guy. Don't forget what you learned as a pilot before you got to XJT. Remember traffic patterns? We still do those. Uncontrolled ops at a smaller field work the same way they did in the GA world. Make the usual announcements in the pattern. When cleared for the visual, it's time to be a pilot. Take charge and make it happen.
Don't be too soft on the controls on final. One of the things you need to do on that first approach and landing is to show me that you know what you're doing. Give me confidence that I won't need to take the controls. This will come with time but probably won't be ideal your first few months. It takes time to settle in to line ops. Just show me that you're trying.
Listen ahead to what the guy in front of you is saying on the radio.
Do the usual stuff as an FO without having the CA have to ask you if you did it (Keep the next flight tasks as a priority over personal stuff, like checking your phone for messages).
Speaking of phones, turn it off before pushback, please.
We don't verbalize everything we are thinking about so it's ok to remind the CA of tasks that need doing (like starting the other engine during taxi approaching the runway; you need 2 minutes with a warm 145 engine before you can push up the TLs).
Oh yeah, what the others said as well...
When in doubt, ASK.