What to Remove before selling Macbook?
The simple solution

Create a new admin account, then use it to delete your personal account(s).

When you delete a user, you have the option of performing a "secure erase" on their home directory:



Assuming you haven't stored any personal files outside of your home directory, this will do the trick.



The paranoid solution

If you want to be really thorough, the only way to ensure that none of your personal data remains is to securely wipe the drive. You can do this from Disk Utility by clicking "Security Options" on the "Erase" tab:



After that, reinstall your applications. None of your personal data will remain.