It all depends on how securely you want to delete your documents. Is this computer one you’ve used for sensitive business-related stuff? Does your company need you to wipe it securely so no documents fall into the wrong hands? If so, then I would suggest searching Google for a secure file deletion tool. Unfortunately, the one I used to use is no longer supported (iWipe). Use the tool to delete all your sensitive documents first, then use a Mac OS X installation disc to format your machine. Install a fresh copy of Mac OS X on your computer using the same disc. Create a simple user called something like, “User” and sell it that way. I would also suggest you use some mild cleaner (water or 409) to very gently clean the metal surfaces to remove fingerprints, dust, smudges, and dirt. Finally, give the screen a good wipe down with a microfiber cloth (available at places like Office Depot, assuming you live in the USA). When you’ve found a buyer, don’t forget to include everything that came with your computer originally, like the power cord, all installation discs, your Apple remote, etc.