Only go to sites that your parents and teachers have said are OK.
Remember never to give out personal information such as your name, home address, school name, or telephone number in a chat room or while texting. Also, never send a picture of yourself to someone you text with without your parent's permission.
Do not meet someone or have them visit you without the permission of your parents.
Tell your parents right away if someone you don't know tries to text or chat with you.
Remember that people online may not be who they say they are. Someone who says that "she" is a "12-year-old girl" could really be an older man.
(adapted from http://www.fbi.gov/kids/k5th/safety2.htm)