Also close the fireplace dampers, so air doesn't escape through the chimney, Lano recommends. And if you set your water heater at 120 degrees – "many are preset at 140 degrees," Lano says – you likely won't notice a difference, but it'll take less power to keep your water hot.
Here are some other easy-to-do strategies you might want to consider, courtesy of Katie Ross, education and development manager at American Consumer Credit Counseling: Make sure your heat vents, registers and radiators are free of obstructions, close doors to rooms you infrequently use and don't run the fan after a shower since that humidity will warm up the next room – at least for a while.
If you're going to be gone for the day, turn down the thermostat. (Most energy experts say it's a myth that it costs more to reheat a home than keep the house in a constant state of warmth.) And remember to clean out your heater's air filter. That's about as basic as it gets, but if you're a new homeowner or newly divorced and your ex used to do it, you may not realize this is a simple chore that can bring your heater to a complete stop if not done. An air filter generally costs between $4 and $15, usually depending on the size and brand; having a heating professional come out to tell you that you need to buy an air filter can cost around $100.
Average cost you'll initially incur: Not a dime.
Corrected on 01/16/2014: A previous version of this story misstated the heat-loss reduction of window film.
Corrected on 01/17/2014: A previous version of this article misattributed a quote about white sales.