Open Facebook and go to your profile
Tap Friends
Find the friend you want to make private
Tap the three dots next to their name
Select Edit Friend List or Manage Friendship
Choose Restricted to limit what they can see
To hide your friends list, go to Settings and privacy
Tap Settings
Go to Audience and visibility
Tap How people find and contact you or Who can see your friends list
Set your friends list visibility to Only me
Save the changes