A storm door can help insulate doors too. And you can always make draft dodgers to lay along your windows. And you can purchase guards for the bottom of your exterior doors that are self adhesive to reduce drafts there. The experts also recommend placing a protective barrier over your AC unit. Make sure you have a fresh furnace filter too. I purchase the cheapest one and replace it each month on the first of the month. If you haven't had your furnace cleaned and inspected in the last two years, it's a smart investment to make before it's really cold.
Don't forget to change the batteries in your smoke and carbon monoxide detectors while you're at it. And add an emergency kit to your home and car, if you don't have one.