Some more good tips from the National Institute for Automotive Service Excellence:
Engine Performance-Get engine driveability problems (hard starts, rough idling, stalling, diminished power, etc.) corrected at a good repair shop. Cold weather makes existing problems worse. Replace dirty filters-air, fuel, PCV, etc. A poorly running engine is less efficient and burns more gasoline.
Fuel-Put a bottle of fuel de-icer in your tank once a month to help keep moisture from freezing …in the fuel line. Note, too, that a gas tank that's kept filled helps prevent moisture from forming.
Oil-Change your oil and oil filter as specified in your manual-more often if your driving is mostly stop-and-go or consists of frequent short trips. A poll of ASE Master Auto Technicians revealed that regular oil and filter changes is one of the most frequently neglected services, yet one that is essential to protect your engine.
Cooling System-The cooling system should be flushed and refilled as recommended. The level, condition, and concentration of the coolant should be checked periodically. (A 50/50 mix of anti-freeze and water is usually recommended.) DIYers, never remove the radiator cap until the engine has thoroughly cooled! The tightness and condition of drive belts, clamps, and hoses should be checked by a pro.
Heater/Defroster-The heater and defroster must be in good working condition for passenger comfort and driver visibility.
Windshield Wipers-Replace old blades. If your climate is harsh, purchase rubber-clad (winter) blades to fight ice build-up. Stock up on windshield washer solvent-you'll be surprised how much you use. Carry an ice-scraper.