Harvest Moon: Give people enough presents and they'll like you. I've actually found this one to be true.
Final Fantasy: Zippers in places they don't belong is actually quite fashionable. Also, don't piss off anyone named Sephiroth.
LoZ: Always break jars when you see them. There's usually something of use inside, and no one really seems to care.
Star Fox: When all else fails... DO A BARREL ROLL! Also, Wolf can't let you do that.
Left 4 Dead: Don't stop and oggle at the scenery. They are coming.
Fallout 3: Start collecting bottlecaps. Like, now.