Social networks like Facebook and MySpace have turned many social norms inside out. Your online friends may not be friends offline—and you may not be exactly whom you claim to be, either. How to approach strangers online, handle unwelcome solicitations, or make real friends out of virtual ones is stuff your parents probably never taught you. Here's how etiquette experts would politely navigate the worlds of Facebook, LinkedIn, and Twitter.

Q: I've got a strict policy about "friending": I invite only people I know well. And sometimes people they know. And occasionally complete strangers whose profiles sound cool. Is there anything wrong with that?

A: Overaggressive friending is the most common social-networking faux pas. After all, these networks were made to facilitate new connections.

Social media consultant Ariel Waldman says that it's usually fine to friend people you don't know just to make their acquaintance. "Otherwise you wouldn't really be networking," she says. But it depends on the service. Friending someone you don't know on Dodgeball (a location-based service that lets you see other users who are physically nearby) is creepier than doing so on Twitter, which doesn't give away users' real-life locations.

In fact, Facebook and LinkedIn automatically suggest people you might know, based on whoever's already in your network. In general, you should already have some kind of link to the person you want to meet—even if he or she is merely a friend of a friend—and a valid reason for making the connection.

Q: I'm scrupulously honest in most things, but my online profile—well, let's just say it's a best-case scenario. Am I required to be totally honest when describing myself?

A: It depends on what you mean by totally. A little embellishment may be OK, but stretch the truth too far, warns Samantha Von Sperling, director of Polished Social Image Consultants, and you'll put your reputation at risk. The solution is to be honest—don't edit your picture so you look like Brad Pitt or Angelina Jolie—but selective about the information you share. For example, Facebook requires that you supply your birthday at signup. But you can hide it: in the Edit My Profile page's Basic tab, select Don't Show My Birthday In My Profile from the drop-down menu.

Don't want Facebook friends to know how old you really are? You can opt to hide your birthday."Saying I'm in my 30s when I'm 37 is fine," Von Sperling says. "But it's not OK to say I'm in my 20s. If I start lying about how old I am, how much money I make, or how much I weigh, sooner or later someone will find out and I will look like an idiot."