That it is important to be virus, adware and spyware free, and that you have run Error Checking, (the old Scan Disk), and Disk Defragmenter, before upgrading to SP2.

Create a Restore Point before downloading and upgrading to SP2. SP2 creates it's own Restore Point, but it is better to create your own.

Many people blame Service Pack 2 for issues that appear with the computer after upgrading. But SP2 does not make these issues, it only highlights issues that existed before the upgrade was attempted.

In short, make sure your computer is clean and tidy before upgrading.