A working heater and defroster are obviously absolute necessities in the dead of winter for driver comfort and window visibility purposes. If your windshield wipers are old, replace them before the snow hits. It takes a lot more out of a blade to push snow and ice off of the car than it takes to push rain off of the car. Winter blades can be purchased that fight the ice. In addition, make sure that your windshield washer fluid bottle is always full. All of that salt and dirt that the plows are putting on the roads will end up on your windshield.
It’s also important to make sure that your lights and tires are in proper working order. There are a lot less hours of sunlight in the winter, meaning that you will be using your lights for visibility and safety purposes a whole lot more. If tires are worn, replace them. If your tires have low pressure or tread you may be able to get away with using them on dry pavement, but you will have trouble driving on icy, wet surfaces.