Proper system maintenance can help your hardware run better by allowing it to find files easier.
Defragment the hard drive(s) often. Loading files is harder for the computer when the file data is not stored in contiguous sectors.
Clearing Temp and Backup Files, temp files can build up and take away storage space and make it difficult for running programs to save their temporary data if there are a large number of unused temp files.
Uninstalling Applications, remove unused applications from your computer, particularly if they are programs that load on startup and stay active in the background. They are just using resources unnecessarily.
Windows Registry, as not all programs uninstall well and may leave registry entries, it is a good idea to Clean the registry periodically. There are several third-party or after-market registry cleaners available.
Service Packs provide updates to reported issues. These could be fixes to problems or refinements to make things run better. Some people load service packs as soon as they are available and others wait until the next service pack after the one they are loading has been released. With the complexity of the software, there is always a possibility of a bug being in a service pack; however, you should look at the release notes to see what has been fixed in each service pack. You will generally be much better off installing a service pack that fixes a problem affecting your day-to-day problems than maintaining an old service pack that is slowing you down.