The most important step in car shocks maintenance is simply to remember that your car has them to begin with. You can tell a great deal about their performance by simply feeling your car's suspension as you drive.
Motor Trend magazine also suggests taking your vehicle out to a secluded parking lot, accelerating to 10 miles per hour (16 kilometers per hour) and hitting the brakes. If the front of the vehicle keeps bobbling after you come to a stop, then your shocks are likely shot [source: Motor Trend].
When you're not on the road, you can get a closer peek by getting on your hands and knees and looking at these ride-softening little gadgets. If you see dents in the shock tubes, leaking oil (though a slight oil film over the lower portion of the shocks is OK), then chances are you're in the market for some new shocks.
You should also keep an eye out for loose mounting bolts and worn mounting blushing, which may also result in a rattling noise while you're driving. Your shock absorbers need a firm mounting to work properly, so you might have to replace loose bolts and blushings. In some cases, this requires the replacement of the shock absorbers themselves as some designs include the blushing as part of the shocks.
Your shocks are just one part of the vehicle's overall suspension system, so you'll want to keep an eye on such components as ball joints and springs as well.
Worn shocks don't just hamper driver comfort; they can harm overall suspension performance and reduce brake efficiency, cornering ability and antilock brake system effectiveness. So when shocks go bad, it's out with the old and in with the new.