Don't talk loud in public. Don't talk or text to someone when you're visiting with someone else. Table manners Movie theatres classroom - using your phone in the right ways Driving
Don't post anything you wouldn't want your grandma to see.
You might not be worrying about college or future employers right now, but a few years from now you might be, and they will be able to see the stupid things you posted because they never go away.
Employers and college entrance people DO look at social networks to get an idea of the people they're considering.
Hoaxes Chain letters or ....repost this now.... cyberbullying