Back up your MacBook with Time Machine or another backup method
Sign out of iCloud
Sign out of iMessage
Sign out of FaceTime
Sign out of any other Apple services or apps you use
Open System Settings
Go to General
Select Transfer or Reset
Choose Erase All Content and Settings
Follow the on-screen prompts
Enter your Mac password if requested
Confirm the erase process
Wait for the MacBook to restart and erase
Set up the MacBook as new or shut it down for the next user