1 Put on a sweater. Grandma's advice holds true. Get everyone in the family to choose a comfy sweater and collect them in a central location for quick changes upon arrival at home.
2 Open blinds and windows during the day and close them at night. Let the sunlight do its job and then when it sets, trap the heat in the house.
3 Put plastic over doors and windows that won't be used. "Storm" door and window kits are available at most home improvement stores, or you can go rogue with some plastic sheeting and a staple gun.