OP, dress nicely, no jeans or sneakers - like you're going out to dinner (but no tits or ass showing). People gave us some religious gifts at our son's naming (bris was at the hospital before we went home from his birth), but many didn't.
Stand when others stand, sit when others sit. They'll announce his hebrew name. Don't worry if you don't understand what they said - half the time I don't either.
Be careful when you're about to eat or drink - a prayer may be said first. Just make sure you're not the first to take a sip or bite. Don't ask to see the penis.