To clean your screen:

WARNING: If you have a flat panel monitor, its softer screen needs extra TLC (tender loving care). Be sure to follow manufacturer's directions.

To clean your monitor case:

For plastic cases - Use a multi-purpose cleaner that is safe to use on plastic. Spray it onto a rag and wipe over the case.

You can use a vacuum hose attachment to clean dust from the vents at the back. 

To clean your tower:

For plastic or metal cases - Clean the tower case like you do the monitor case.  Spray multi-purpose cleaner that is safe for plastics or metal onto a rag and wipe it clean.  The really important parts of the tower are the back and the inside.  The back of the tower can get very dusty.   It’s practically a dust magnet!  All that dirty stuff can clog  vents and shorten the life of your computer.  Spray away the dust with canned air or carefully vacuum with a soft brush attachment.    

Now for the inside: your parents or teacher should clean that part.  Remind them to unplug the computer first to be safe.  Use canned air to blow all the dust away.  Be careful not to bump anything loose in there.  The inside doesn’t have to be cleaned very often, only about once a year.  Don’t forget though.  You’ll be surprised at how much dust can get in there.

To clean your keyboard:

Clean the keyboard when the computer is off. First it’s a good idea to use a can of air to blow out any dust and dirt that has settled down around the keys.  Look closely around the space bar.  Do you see yucky, dirty stuff down in there?  That’s when you need a can of air, or you can use a vacuum with a hose and brush attachment.  Then use a multi-purpose cleaner like you do on the monitor case.  Lightly spray the cleaner onto a rag and wipe around and over the keys until they are clean.

To clean your mouse:

Clean the mouse when the computer is off. Use a multi-purpose cleaner that is safe for plastic.   Lightly spray it onto a rag and wipe over the mouse.  Sometimes you need to clean the bottom of the mouse where the ball is.  If  your mouse hasn’t been working smoothly, cleaning this area could help.  Press easily on the round cover surrounding the ball and twist it.  That pops it off and let’s the ball come out. Wipe it off with a lint free rag.  Look down into the hole where the ball sits. There are little rollers in there that can get tiny strands of gunk twisted around them sort of like a vacuum cleaner does sometimes.  If you see any dust or lint, pull those out. Lightly spray cleaner onto a rag and wipe this area clean.  Put the ball back, and twist the   cover back on.

To clean your floppy drive and CDs:

To Keep Your Computer
Working in Tip -Top Shape

"Scan & Defrag" and
delete temporary files

occasionally.

Running a scan, Disk Scan, checks your hard drive for errors.
Defragging, using Disk Defragmenter, rearranges files and unused space on your hard drive so that it will operate more efficiently.

Both the scan and defrag will improve the computer's performance.

Temporary Internet Files, also known as "cache" (pronounced - cash), build up over time. They are little bits and pieces of web pages you visit. Their purpose is to put a small amount of that site on your computer's hard drive so that the next time you visit that web site it won't take so long to load everything. Eventually you can build up too much cache, as strange as that sounds, and ironically it can instead slow down your computer. So clear the cache once in a while to remove all those bits and pieces. They are Temporary files, files with a .tmp extension. To find them you can go to the Start Menu, Search, Files, and search the hard drive (C:) for *.tmp. The star is a wildcard, meaning it will find anything in its place. The way it's used here, it will search for any filename as long as it has the temporary file extension, .tmp. Then you can delete the files it finds. WARNING- NEVER delete any file unless you are sure you should. It's also a good idea to only delete files, not folders.
Another method for clearing the cache is to use the Options area of your browser. In Internet Explorer it can be found under Tools in the Menu Bar or you can right-click the browser's icon and choose Properties. Then look for the Temporary Internet Files area. Click the Delete Files button there to clear the cache.