DON'T ever be mean or rude online. You could get kicked off that website.
Keep your passwords to yourself. They can hack your account and do bad things.
Don't meet anyone offline you don't know. You could get hurt or kidnapped.
If you get an email from someone you don't know don't open or answer it. It could send a virus to your computer.
Be careful what you post. Don't post pics while your doing what that pic is of cause people could find and hur you.