Pictures can stay alive forever
Remember that anyone can save a picture you've shared publicly! Just because you share it "Only with Friends" or through an app like Snapchat, people can still take screenshots of your pictures and continue to share them with others. Once you send that picture, you can't take it back.
Post pictures cautiously.
Check with your parents before you post pictures of yourself or others online. Do not text or post inappropriate pictures of yourself or others. Even if you "take them down" someone, somewhere is likely to have a screen shot that they will share with others.
Protect your passwords.
NEVER share your password with anyone, including your best friend. The only people who should know your password are your parents or guardian.