Using a social network could be a terrifying thought for many educators due to the sharing of personal information. My one piece of advice is that you use a different account when you are connecting with students, parents or other teachers around the country and world. I personally use Facebook to communicate with my students' families. Twitter and Pinterest are what I use to connect with other educators.
The easiest way for educators to get relevant and free professional development is by following other teachers on Twitter. There are also weekly Twitter Chats were educators discuss school issues that range from technology to mental health of students.