Don't let it get to you.

Tell an adult/friend before it gets worse

Delete your account

Don't put you're school, address, friends and information on social networking sites because you're literally telling people (good AND BAD) where you are...

Don't tag people in photo's without their permission (definitely if you have a public account) they might not want to be tagged in a photo anyone could see.

When you choose your password, pick something you'll remember, unique and to make it more secure, you could make it longer and include numbers to ensure you can't be hacked. :)