A computer like all the other house hold articles should be cleaned once in a while. The frequency by which it should be cleaned depends upon the environment it is used in.
If the environment is kind of dusty where more people walk in and walk out the computer has to be cleaned once every two months. If it is in an isolated environment, it is good to clean it once in 4 to 6 months.
For cleaning LCD monitors, be careful as the panel is quite thin. Improper cleaning could do harm. It is always good to clean your monitor with a soft dry cloth which is not wet. That should do just fine.
For the outer of a CPU case, use a soft cloth .Make sure that the cloth is not too wet.
Do not use vacuum cleaners to clean as they may damage the vital components of your computer.
For cleaning the inside of a CPU, you can make use of a soft dry brush for cleaning purposes. Be very careful and avoid contact of moisture with the internal components.
Clean your speakers, your keyboards and other utilities. Use a soft dry brush to clean the dirt in between the keys.
Clean your CD-ROM drive by getting a good CD lens cleaning tool from any computer shops near your house. The lens cleaner will resemble a CD with brushes fitted in it. It will come along with a small solution.
Always clean your computer for a longer life and a good look.