Do you want to keep your Mac running great with less chance of problems occurring? Follow this advice and you will have fewer problems and headaches.

Set a maintainance schedule.

Weekly
a) Backup important folders/files. If nothing else, backup the System Folder, bookmarks, e-mail address book, and any documents.
b) Check the web sites of your software vendors for updates to software you are using. Make sure they're compatible with the Mac OS you have installed before applying any updates.

Monthly
a) Run Apple's Disk First Aid & Symantic's Norton Disk Doctor &/or Micromat's TechTool Pro.
b) Run Alsoft's DiskWarrior.
c) Rebuild the desktop with TechTool Pro or TechTool Lite 3.0.1 (make sure to use the save button the first time).
d) Back up the entire hard drive and make a second backup to store off site.
e) Run your virus software. I use Virex but there are other products available such as Norton AntiVirus.

Every 6 months
a) Zap the PRAM with TechTool Pro or TechTool 1.2.1 (again, use the save button the first time).
b) Reinstall the hard drive driver with Drive Setup (or whatever utility you use for this).
c) Trash the 'Finder Preferences' in the 'Preferences' folder in the 'System Folder' on the hard drive. Then immediately restart and empty the trash. Now reset control panels that have defaulted such as 'Date & Time', 'General Controls', 'Memory', and 'Mouse'.
d) Defragment the hard drive with Norton Utilities or TechTool Pro or Plus Optimizer (this comes free with DiskWarrior CD). I recommend using Plus Optimizer and disabling the Optimizing function in Norton and TechTool Pro.

Yearly
a) Clean out the 'Preferences' folder for any applications you no longer use by trashing the related preference file(s). If you're not sure, then put the file(s) in the trash. Now restart the computer and test your applications to see that they run fine before emptying the trash.
a) Open the computer case and blow out the dust with compressed air.
b) Clean the mouse ball and rollers. Use Q-tips moistened with rubbing alcohol on the rollers. Never use sharp objects. Warm water and liquid soap for the ball is fine. Completely dry before reassembling.
c) Clean the keyboard with compressed air and a moist Q-tip and non-abrasive cloth.
d) Clean the monitor case and screen. Follow instructions in the monitor's manual. Never put liquid directly on the screen; use a moist non-abrasive cloth.