Run Disk Cleanup & Disk Defragmenter at least once/month.
Disk Cleanup: Frees up disk space
Disk Defragmenter: Organizes files for optimum speed
Utilizing the "Favorites" toolbar in Windows 7 will allow you easier and quicker access to folders and files. This video is specific to Windows 7.
Utilizing the "Document Links Toolbar" in Windows XP can make saving documents in specific folders quicker and easier. This video applies to Windows XP only.
Downloading and using Windows Desktop Search can help you to find files and e-mails quickly and make you more productive.
Using the Search feature included with Windows 7 can help you find folders, files, documents and e-mails quickly.