Decide who can contact you

Head back to your privacy settings now (where you were to change your default privacy) to choose who can contact and interact with you on Facebook. Under 'How you connect' you'll find options on things such as who can send you Facebook messages and friend requests, and also who can post and see posts on your Timeline. This means you can be invisible on Facebook except from friends you have already accepted, hide your wall from certain friend lists, and only allow friends of friends send you friend requests.