Before you let go of your Mac

When preparing to sell or give away your Mac, you should wipe your hard drive. These steps show the recommended sequence of actions:

1. Deauthorize your computer from iTunes, if applicable.
2. Back up your data using Time Machine or other backup methods which SuperDuper is by far my favorite which will create a bootable backup on an external drive that you can boot off if your later remember you needed something off that old Mac.
3. If you use Find My Mac or other iCloud features on this Mac, complete these steps:
   1. Back up your iCloud content.
   2. Choose Apple Menu (?) > System Preferences, then click iCloud
   3. Deselect the Find My Mac checkbox.
   4. Sign out of iCloud. When you sign out of iCloud, you're asked whether you want to remove iCloud data from your Mac. Removing iCloud data in this way makes sure that the data isn't also removed from any of your other devices that are using the same iCloud account.
4. If you're using OS X Mountain Lion v10.8 or later, sign out of iMessage:
   1. In the Messages app, choose Preferences > Accounts.
   2. Select your iMessage account, then click Sign Out
5. Reformat your hard drive and reinstall OS X. Here are some instructions on How to Erase and Reinstall OSX
6. After you reformat your hard drive and reinstall OS X, the computer restarts to a Welcome screen and asks you to choose a country or region. If you want to leave the Mac in an out-of-box state, don't continue with the setup of your system. Instead, press Command-Q to shut down the Mac. When the new owner turns on the Mac, the Setup Assistant will guide them through the setup process.