The first step you need to take is to turn off your following option from Facebook that no one can follow you anymore. Following is already enabled for your friends as they are on your friend list, So you can't actually stop your friends as your followers until you don't delete them from your Facebook friend list.
Lets come out to the point how you can easily disable the following option for public:
Step 1: Click the Down arrow sign from top right on your window and click Settings from the menu.
Step 2: Select Followers from left side menu.
Step 3: Now change Everyone to Friends on who can follow me.
You are done! now none can follow you expect your friends.