Buy a virus-scanning software package and keep it updated to detect new viruses. Never delete programs manually. When you install a program, it inserts files and information all over the place. To delete a program and all associated info, use the uninstall utility that came with the program. Update your programs, especially your virus checker.
Many software companies provide updates on their websites.
Keep it clean. Each year, open up the computer case and clear out the dust that will accumulate. For more on keeping your PC clean, go here Shut down gracefully. Make a point of always using your computer's shutdown command, and wait until the computer notifies you that it's safe to shut down. Improper shutting-down can leave messy file fragments that can clutter up your hard drive and confuse your system.