Two-factor Authentication - "something you know, and something you have" - is the number one thing you can do to protect yourself online.  While this used to be a complex and difficult process to setup and utilize, it has now become a relatively common and simple affair thanks to the ubiquity of smartphones and "authenticator apps".  

Lifehacker has just updated their excellent article titled "Here's Everywhere You Should Enable Two-Factor Authentication Right Now"

Check it out, then immediately go and turn on two-factor everywhere you can!  You'll be thankful when the next huge security breach of a major website happens.