First, go into your settings tab, and click "security and Privacy". YOU ARE ALSO ABLE TO BLOCK PEOPLE IF THEY ARE HARASSING YOU, AND CHECK WHO YOU HAVE BLOCKED BY GOING INTO THE "BLOCKED PEOPLE" TAB.
Once you are there, you can change your settings according to who you want to allow photo tagging and whether you want your tweets to be protected. You can also change your discoverability, if you want to be found by your email address or not.