Profile Picture Customs

• Your profile picture is your first impression on the rest of Facebook. Always err on the side of respectability. Make your profile picture something that you wouldn't mind your mother, or a future employer, seeing. Avoid profile pictures of you being drunk and disorderly, and definitely avoid profile pictures of you going shirtless, or pointed down a plunging neckline.
  
  

Privacy Revelations

• Facebook makes its money off of getting its users to share personal information -- this is what drives its advertising, and why the company seems to make its privacy settings inflexible. Spend the time to carefully examine Facebook's privacy settings and choose what you do and do not share on the service. Also be aware of your status updates and comments might be interpreted by other Facebook users. Ordinary text without some careful thought put into it can be seen as cold, harsh or vain.
  
  

Family Information

• Facebook will encourage you to connect to as many people as you know; it's how they make money. Be aware of the implications of this. Just because you state yourself as publicly married doesn't mean you have to link to your spouse. Just because you've got kids doesn't mean you have to post pictures of them, publicly, or list their ages. While Facebook's custom is to share everything and link to everyone, it's worth it to ask yourself, "Why do does everyone need to know this?" before doing so when it comes to personal and family information.
  
  

Interesting Posts

• The whole purpose of Facebook is to allow users to share things they're interested in. This is one case where the Facebook custom of "share everything by default" can give you tangible business and personal benefits, like networking for job-hunting, and helping employers learn more about you. That said, don't overdo it, and do try to keep what you post relevant to your interests and the interests of your friends.
  
  

Replying To Posts

• Before you hit that send button, double-check your post to make sure it's relevant to the original topic you're replying to. Then decide if that post needs to go to a single person, or if it needs to go out in public. Deciding when to single-cast and when to broadcast, is part of the social milieu of Facebook.