There are a few things you might want to do when you want to sell your Mac Pro computer. It is a good idea to make a backup of all of the data you want to retain, such as your pictures, videos, music, documents, and other such files. There are different ways in which you can perform a backup. You could hook up a compatible external hard disk drive or use several larger capacity USB thumb drives.
Just make sure the storage drives use the correct hard drive format, such as FAT, so your data can be transferred. For instance, if your external hard drive is in NTFS format, you will need to reformat it to a different one able to be recognized by the Mac operating system. Also remember, formatting a drive does erase any existing data from it, so verify the drive is empty or contains data you no longer want before you start the format process.
To format the drive, you can use the Disk Utility program from within your Mac Pro operating system. Depending on your version, the number of different format choices could vary. In Mac OS X, you typically are presented with 5 different options. Out of the five, the most widely used formats are ExFat, MS-DOS (FAT), and Mac OS Extended (Journaled). If you are only going to be using the external drives with other Macs, then the Mac OS Extended (Journaled) format is fine. Otherwise, if you intend to share files between Macs and Windows PCs, then you should choose one of the FAT options.
After your data is completely backed up, it is a good idea to run a full-system restore to reset your Mac Pro back to its original out-of-box settings before you sell it. This process will wipe all of your data from the computer and remove all personal information.