Earlier, I suggested using Disk Utility's Repair Disk feature to preemptively check for and eliminate common disk gremlins (see Run Disk Utility). Because disk errors do creep in during ordinary computer use (seemingly of their own accord), I suggest running Disk Utility and using its Repair Disk command once a month.

Why Do Disk Errors Occur?

In addition to Disk Utility, numerous third-party utilities check for, and attempt to repair, a wide range of disk errors. I've run these utilities hundreds of times over the years, and a shockingly large proportion of the time they've found and fixed errorseven though I wasn't aware of any problem. What causes these problems in the first place?
Although I can't give you a complete answer to this question, I can offer a few reasons some disk errors occur:
Buggy software: Virtually all software contains some bugs, and bugs can cause bad data to be written to your disk or can corrupt existing data.
Hardware failures: If your hard drive, logic board, or various other components have manufacturing defectsor develop malfunctions later onthese can result in disk errors.
User error: If you unplug an external hard drive without unmounting the volume(s) first (File > Eject), you may interrupt the flow of data to the drive, or interrupt a housekeeping procedure. Many other user errors can also result in disk problems.
Power failure: If the power goes out (or your battery dies) at an inopportune moment, a file may not be written properly.
In other words, stuff happens. You can guard against some problems simply by being careful, but stuff will still happen.

Clean Your ScreenYour computer's display attracts dust, and over time that can impair the screen's readability. (It's also, let's face it, just yucky.) Once a month, or whenever you can see a thin layer of dust on a black screen, give it a quick cleaning.To clean a screen, use a soft, lint-free clothnot a paper towelmoistened slightly with water to prevent static buildup. You can also use cleaning solutions designed expressly for computer displaysI've had good results with iKlear screen cleaning products from Klear Screen (www.klearscreen.com)but avoid anything containing alcohol or ammonia. Wipe the screen gently; LCD displays, especially, can be damaged by excessive force.

Clean Your Mouse or Trackball

I spent five years working for Kensington, a company that made its reputation in the Mac world by selling fantastic mice and trackballs. During the time I worked there, we saw the computing world transition from opto-mechanical devices (in which a ball turns slotted rollers connected to wheels whose speed and direction were measured with photosensors) to purely optical devices (in which a tiny camera tracks changes in the texture of your desk's surface, or the trackball's surface).
The biggest and most exciting advantage of optical designs was supposed to be that they never had to be cleaned. Gone were the old days of disassembling a mouse, losing the ball as it rolls across your office floor, and fumbling with cotton swabs to clean dirt and hair off of tiny rollersa procedure you might have to repeat every few weeks or so. Optical mice have no moving partsno rollers, no ballso cleaning should never be necessary.
Experience has shown that although optical devices require less cleaning, they still require some. Specifically, optical mice tend to accumulate dust inside the opening at the bottom (often shaped like a keyhole) through which the sensor watches your desktop. If it becomes clogged, your pointer may move erratically, or not at all.
Optical trackballs have a similar opening above the lens (remove the trackball from the casing to see it) with a similar tendency to attract dust. In addition, the tiny bearings or rollers on which the ball rests can collect dust and hair, preventing the ball from moving smoothly.
And, of course, plenty of Mac users still have older pointing devices that use the ball-and-roller mechanisms and therefore require what we now think of as old-fashioned cleaning.
Your input device most likely came with cleaning instructions, so I'll simply say: follow them now. If you don't have the instructions (and can't find them on the manufacturer's Web site), they generally boil down to removing visible dust and gunk from wheels, rollers, bearings, and other moving parts (and away from the openings used by optical sensors). A slightly moistened cotton swab will do the job nicely.

Tip

Cleaning Mighty Mouse's Scroll Ball. The miniature trackball that enables you to scroll with an Apple Mighty Mouse can accumulate dirt, leading to poor scrolling performance. You can't remove the ball, but you can generally dislodge any dirt by inverting the mouse, pressing the ball inward as far as it will go (it springs inward slightly), and rolling it vigorously in every direction. If scrolling is still not smooth after you do this, repeat the procedure using a slightly moistened cloth or paper towel.

For most people, once a month is a reasonable cleaning interval. If you have pets, you may need to clean your mouse or trackball more frequently; if you work in an Intel clean room, maybe never!

Exercise Your Notebook's Battery

Early portable computers used NiCad batteries, which were subject to the dreaded "memory" effect. To get maximum run time from them, you had to discharge them completely before recharging them; if you failed to do this, even a fully charged battery might suddenly run out of power after a short time.
The lithium-ion batteries used in modern Mac notebooks (and iPods) don't suffer from memory, but according to Apple they still need to be "exercised" (that is, discharged and recharged periodically) for maximum performance. If you leave your notebook plugged in all the time, the battery never discharges beyond a few percentage points, so it gets insufficient exercise. For such users, Apple recommends that once a month you unplug your computer, run it on the battery until it discharges completely, and then recharge it.
For more information about Apple's notebook batteries, check out www.apple.com/batteries/.

5. Perform Yearly Tasks If you've ever looked around your home and thought, "It's time for a good spring cleaning," you know the value of decluttering. On your computer, as in your home, make an annual ritual of removing dirt, tossing out junk, and putting your belongings in order. Besides giving you a cleaner, more inviting environment, these yearly tasks can extend your computer's life span and help keep your data safe. De-Dust Your Mac

Nearly all Mac models employ one or more internal cooling fans. Without them, your computer would overheat, leading to crashes, erratic behavior, and possibly even permanent damage to sensitive components.
But as the fans pull air into the computer, they also pull in dust. Dust can accumulate on the air intake vents, on the fan itself, or on any surface along the flow of air within the computer. When a layer of dust sits atop a hot component, it acts as an insulator, preventing some of the heat from escaping into the air. And if dust blocks the air flow, the heat that does escape has nowhere to go. Either way, your fan must work harder, which not only makes it noisier but also makes it suck in even more dust.
In short, dust is no friend of computers. By the simple act of getting rid of the dust, you can make your Mac cooler and quieterand prevent all sorts of unpleasant problems.
You can remove dust by brushing or wiping, by vacuuming, or by blowing it off with compressed air. The compressed-air approach is the least desirable, because it puts the dust right back into the air. I prefer an ordinary vacuum cleaner with a hose attachment, but before using such a vacuum on the inside of your computer, take note of the warning just ahead. If you choose the brushing or wiping approach, be sure to use a soft, dry cloth or a soft, dry brushand a gentle touch.
Warning! Conventional AC-powered vacuum cleaners, particularly those with plastic nozzles, can in theory build up enough static charge to damage your computer's circuitry if used on the inside of a case. For vacuuming the inside of a computer, use either a battery-powered vacuum or an antistatic vacuum designed expressly for cleaning electronic equipment. In any case, be careful not to touch the nozzle to any components inside your computer.
To de-dust your Mac, follow these steps:

These remaining steps are for desktop computers only:

Clean Your Keyboard

Before you put away that vacuum cleaner or canned air, give your keyboard a once-over too, following these steps:

Clean Your iSight

If your computer has an iSight camera (either built in or external), this is also a good time to make sure it can see you clearly. Follow these steps: