1: Stay out of trouble!
2: Have fun
3: Dont worry to much about tactics and boatspeed in the beginning.

Concentrate on the boats around you, see what they do and what pays off, and stay out of trouble. Nothing is worse for a new crew than to be in the middle of a "situation". Nobody is a world champ in the first attempt, so go out there to have fun. Later on, if you get serious about racing and develop ambitions, it still pays off to keep focused on having fun while practicing and racing. The day it's no fun anymore, you will probably quit racing..

(To stay out of trouble, some basic knowledge about the racing rules are neccesary, like port/starboard, windward/leeward etc)