1) Check Tyres
Tyres are the single most important part of your car. They have an enormous impact on performance
and safety, and they're one of the few components on your vehicle that can kill you if you ignore them. A worn or underinflated set of tires can be detrimental to handling and braking and can lead to blow-outs at speed. If you own dedicated sets of winter and summer tires, inspect both sets of rubber as you swap them out for seasonal duty or storage. Even if you use all-season tires, check for bubbles in the sidewalls (usually a sign of broken belts in the tire's carcass), uneven wear, or visible wear bars. If you see any of the above, replace the tire. Be sure to look out for missing balance weights — the clip-on or stick-on lead/steel weights that mount to the edge or inside of your wheels. While you're at it, make sure that your spare tire is properly inflated.
Winter traffic is often much slower than summer traffic, and once Jack Frost shows up, your brakes
see a great deal of abuse. Brake pads often suffer extreme thermal cycling — massive temperature changes due to the high heat of use meeting with freezing water or deep puddles. Removing your wheels often helps with a brake inspection. If you're technically inclined, remove your brake pads and check them for significant wear and cracking; if you're not, make sure that their edges aren't crumbling or heavily discolored and that the your brake rotors or drums have no significant cracking. If you see anything suspect, hit up your mechanic to double-check and/or replace anything that's worn.
3) Get a wash
Winter takes a toll on every part of your car — everything from your brake lines to your engine gets
blasted by a constant barrage of salt, ice, water, sand, and general filth. Interiors become filled with dirt and tracked-in grime. Do yourself a favor and clean your car top to bottom, inside and out. Use good, high-quality cleansers and high-pressure water on the outside to get rid of salt and trapped sand, and be sure to hit the wheel wells and underbody. Clean all that junk out of the trunk and remove litter from under the seats. Vacuum and wash the funk-filled carpets and clean the inside of the windows, which have undoubtedly been smudged when the defroster couldn't keep up and you used your hands to carve out a peephole. Also take time to properly wash and treat the engine bay. It may sound unnecessary, but it's much easier to diagnose leaks or aging parts when everything is clean.
4) Oil Check
Pull out your car's dipstick and check the level and color of the oil — if it's still a pleasant shade of
amber and meets the fill mark, you're fine. If it's amber but low, top it off. If it's black and nasty, change it ASAP. Regular oil should last 4000-5000 miles with no problem; synthetics should go for 6000-7000 miles between changes. (Both of these are general guidelines and vary with driving style and climate.)
5) Cool Coolant
Inspect your coolant level and coolant mix. The overflow or radiator tank should be full, and a coolant
tester available at any auto parts store will tell you if the water to ethylene glycol ratio (the green or orange stuff) needs to be adjusted for maximum cooling. Change your coolant at least once a year for maximum performance. Just make sure that Fido isn't around if you spill some — dogs love glycol's sweet flavor, but it's toxic if ingested.