Here are some tips on what not to do on facebook:
Don't make your status ultra-dramatic. Changing it from "_______ is so in love" to "_______ just wishes it would end" in one day is stupid.
Avoid posting a relationship status as long as possible. You'll look bad if you are constantly going from "In a Relationship" to "Single."
Don't make your profile picture "sexy." If you pose shirtless, flexing/kissing your muscles, taking a picture in the mirror wearing almost nothing, or take a cleavage-revealing self photograph, you won't look so appealing and people will avoid you on the "People You May Know" or regret adding you as a friend.
Don't take every quiz you come across. Filling up every one's home page news feed with your pointless quizzes like "What color should your eyes be?" is obnoxious.
Don't invite people to Knighthood/Ninja Wars/Kidnapping games. Especially if you don't know the very well. Chances are, if you knew them well, you'd know they didn't want that junking up their facebook.
These are just a few tips, I'm sure I'll come up with more as time goes by.