Just as you should check your smoke detectors' batteries every autumn, preventative procedures can keep automotive disaster from striking. The weather can change overnight -- the Colorado Rockies (both the mountains and the baseball team) often get snowed on as early as Labor Day. Applying the infamous Boy Scout motto to colder-weather motoring can make the difference between getting there and back or not.
Year-round routine maintenance is the best way to make your vehicle perform stronger and live longer. The regimen should include tune-ups and inspection/replacement of worn belts and hoses. As the weather cools, consider changing to synthetic lubricants, which work across a wider temperature range than conventional oil. These high-tech oils cost more, so an alternative is to use lighter-weight oils in colder weather.
Consult your owner's manual for proper coolant mix, which is often about 60/40 antifreeze to water. Another trick is to install a higher-temperature thermostat. This will improve heater performance and help the engine warm up faster. (However, some computer-controlled vehicles might not be compatible with non-factory-temperature thermostats.)
Since the heater and defroster work off the cooling system, check heater hoses while inspecting the radiator hoses. Coolant on the floorboard is one common sign of a leaky heater core. Also, vacuum/blow all leaves and debris out of the ducts.
If your battery has removable caps, make sure that all cells are filled with distilled water. Keep all battery terminals and cable ends clean. When jump-starting, never connect the jumper cables' ground clamp to the dead battery's negative post -- use an engine-mounted bracket as the grounding location. In colder weather, this can keep a frozen battery from exploding.
Keep the gas tank as full as possible. Aside from the obvious, this limits condensation in the gas tank to minimize water -- which can freeze -- in the fuel line. "Antigel" additives are available, particularly for diesel-powered vehicles. On non-fuel-injected cars, keep the choke/carburetor butterfly lubricated so it won't stick.
Check the wiper blades for deterioration and consider upgrading to winter/snow blades. "Park" blades before turning off the vehicle or lift them off the glass so they won't freeze overnight. Fill the squirter reservoir with winter fluid, and never put hot water on a cold windshield.
Waxing -- particularly with a carnauba-based product -- will help the paint withstand road salt and other foul-weather grime. Lubricate door hinges with silicone spray so they won't squeak when the weather changes. Spraying the locks and weatherstripping will help keep doors and trunks from freezing shut.
Air condenses in cooler weather, and we're all well educated now on the hazards of underinflated tires. Keep them inflated to the manufacturer's recommendation on the sticker found in the glove box or doorjamb. Check condition/inflation of the spare. Store snow tires horizontally during the off-season to prevent "flat-spotting." Practice-fit snow chains before the weather turns nasty.
Finally, the automotive aftermarket unveils an array of cold-weather solutions every autumn. For cold-country residents, products are designed to heat almost every aspect of your vehicle: from its coolant to its oil to its battery to it locks to its rear-seat occupants. Plan ahead and minimize the stress of foul-weather driving.