Go slow on RP's, if it goes from page 2 to page 8 in a weekend, you're going way too fast.
Give some backstory!!!!! Can't stress that enough!
Don't make an UBER character!
Don't be a blindingly, beautiful, female who is the world's greatest assassin, or a super, tough, guy who can pick up Deathclaws and throw them.
Anyone else who has advice, please post it here.