Computer maintenance is recommended for those who want to keep their computer running at its best, it can be broken down into 2 main areas. Physical and Software based..
Physical means to clean the various external components such as the tower, monitor, printer, scanner, mouse and keyboard etc. Or the internal components of your computer case
Software maintenance is the regular virus scanning, spyware/malware scanning, defragging and backing up of critical data that we all should do
Maintaining your computer properly can help prevent major problems and should be incorporated as part of a semi regular schedule. I am not going to tell you how often you must clean it but more towards what you can do to keep it clean and running.