These seem obvious but in my ventures into the social networking realm of Myspace and Facebook, kids give out way too much information and may put themselves at risk. I try to be cautious with what I put out into the open Internet realm.
1) Don't give out personal information (one or two tidbits of information can lead to finding lots more)
2) Tell your parents immediately if you find information that make you uncomfortable
3) Never agree to meet someone in person without checking with your parents and having them present at the meeting
4) Never send anyone a picture or anything else without checking with your parents (this could exclude friends from school or church)
5) Do not respond to any messages that are mean or otherwise make you feel uncomfortable
6) Talk with your parents so that you can establish guidelines for being online
7) Do not give out your password to anyone other than your parents (even you BFF Jill)
8) Check with your parents before downloading or installing software or anything else on your computer (I would also add, be careful which widgets you add to your profiles, some computer code can provide back-door access to your profiles)
9) Be a good "citizen" in the online world and report anything that seems suspicious or could hurt someone else.
10) Kids, Help your parents understand how to have fun on the Internet and talk with them about what you are doing. Parents, be learners and let your children talk to you about the technology (don't be afraid of it, communicate your concerns with your child and realize that if you are too hard on them they may find alternate ways to setup an online account without your knowledge).
Adapted from: Kids' Rules for Internet Safety
Federal Bureau of Investigation (Cyber Division) of the United States Department of Justice: A Parent's Guide to Internet Safety
Looking at Child Safety on the Internet (ppt file on legislation and case study)
Internet Censorship and our First Amendment (ppt file on legislation and case study)