We can teach students to "THINK" before posting. Asking effective questions such as these will spur some great conversation and give students some things to ponder before posting, commenting, or creating something they may regret later.
You can show the video clip from
http://www.cybersmart.gov.au/Indigenous/I%20need%20to%20know%20about/Digita...This webpage features the tagline "Online business is everyone's business." This concept and the idea that everything you post comes back to you like a boomerang is a great way to help kids think about how what they say and do on the internet may affect them for good or ill in the future.