1. Download the installer from the App Store but do not install it, close the installer when it launches
  2. Format an 8GB+ USB Drive in the GUID type and Journaled (not case sensitive) partition
  3. run the command (where Untitled is the name of the partition you created in step 1): sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app --nointeraction
  4. Sit back and relax, smoke a pipe while you wait maybe