I'd ask what the "house rules" are in case they do anything odd.
Pay attention when the first person deals. Do they burn a card (deal one face down) preflop, and before the turn and river (they should).
Be careful not to flash the bottom of the deck when dealing and practise shuffling before you go so you are confident and don't fumble.
Don't worry if you turn a card over when dealing, it happens. Someone will sort it out.
When you bet, say out loud "raise" if you are raising and call if you are calling it saves a lot of trouble if people are tight about complaining about string bets. A string bet is when you put some chips in the pot ie call, and then add a few more in a second movement, the idea is you might be fishing for information.
Mainly just relax and remember they all played the first time once as well.