Start a Twitter account that focuses on following educators. (THIS IS A MUST!)
Build a circle of connected educators on Google+.
Follow education blogs (read and comment).
Follow education chats that are specific to your content area.
Join and participate in education groups on Facebook and LinkedIn.
Accept invitations to collaborate.
Remember that the purpose of a PLN is personalized learning. You determine your needs and goals, and then acquire the sources that you need in order to attain them.