I've done a few lines now as a relative newbie and really enjoy it. Below are my observations...
Hopefully the ref will give a clear briefing of what they expect from you. If you are not sure, ask. I did and it really helps.
Keep focused and when it looks like an attack is going to break, be prepared. It's very hard to make up the ground if you are flat on your feet. They'll be down in the corner while you are still near the centre circle!
I was very lucky to be AR with an L2 ref a couple of weeks ago - it was a real eye opener the amount of non verbal communication that goes on with a really high quality ref. It really made my job so much easier and the shared confidence of working effectively together. With lower level refs there still need to be plenty of eye contact. You will either need to follow their lead or they will be looking to you so they can follow yours.
The bit that I found hard transitioning initially from being a regular CAR to a NAR is flagging for fouls. I forgot that I could. Use the period at the beginning to gauge the Ref's tolerance level and try to match.
Signal, be confident, hold your signal until its been acknowledged. Get into position and signal, don't try to run and signal.
I hope it helps. Still new so if anyone more experienced thinks I've got stuff wrong, let me know as I'll keep on getting it wrong