1. Make a list of the people that you actually care to stay in touch with for social reasons (for professional connections you already have LinkedIn). Ensure you have other lines of communication open with them (email, IM, text, phone, Skype etc). If possible, and if necessary, inform them you're leaving FB and how you intend to stay in touch with them

2. Delete your FB account. Delete the app from your phone (if you have it)

3. Mark any email from FB as spam

4. Block all FB domains at the router level