Be aware of exactly how cold it is, including the wind chill factor. A doghouse is good to have but may not protect them from frostbite on their extremities. Be sure to bring your pet in out of the cold. Put down a warm blanket for them to sleep on, since tiles can be cold. You can also purchase beds made for dogs at your local pet store.
Another misconception is that snow is a substitute for fresh water. Make sure that your pet always has fresh water available to drink, regardless of the weather conditions.
Fur can provide a measure of warmth for your pet, but fur that is long can also pick up clumps of snow and ice, making it uncomfortable for them. Trim the areas around the paws to keep this from happening. Dogs with short hair don't get the same level of warmth as dogs with long hair. Buy them doggie sweaters or knit one yourself. They will keep your dog warm and make them look even more adorable.
Many areas salt icy streets to provide traction. This salt or deicer can be painful to dogs, if they get into cracks in their paws. By rubbing a thin film of petroleum jelly on the bottom of their paws, it will lessen the amount of salt that sticks to them. When you get back home, be sure to clean their feet so that they will always be able to walk comfortably.
Damp fur can be uncomfortable for your pet. When coming back from a walk in rainy or snowy conditions, be sure to dry them off, preferably with a blow dryer. The cold of winter can be just as dangerous to your dog as the summer heat. Use common sense and keep him or her safe and warm.