Twitter / don't continuously follow and unfollow Twitter users. It gets noticed and sends the wrong message.
Facebook / don't want your photos to be viewed by the entire world? Go to 'Activity log' (under the triangle at the top right). Select 'Photos of you' under 'Photos' and change who you want to see your photos under the 'Shared with' drop down menu.
Instagram / Did you know you can follow Instagram's Instagram page? Well, you can! If they notice you then get prepared for LOADS of followers!