First and foremost, have fun, and make it look like you're having fun.
Get to every breakdown/tackle, and don't tolerate defenders trying to slow down the ball.
Don't be too concerned with secondary signals, a good portion of the time you will not have time to make them.
Any screw-up at kick-off (not 10, out on the full, ball goes in-goal) is a free kick on the halfway.
At scrums, make sure that the props bind onto the hooker, and not each other. Also, kicking the ball *forward* out of the scrum is a penalty.
If the weather is going to be warm, grab a jar of pickles and some Pedialyte, and start drinking more water *now* to make sure you're hydrated. If not, you will cramp up.