Soak up some rays
The sun keeps the whole world warm—why not take advantage of that free energy in your own home? Leave your shades open during the day to let in as much sunshine as possible. (Related: Here are more ways to save on every household bill.)
But close your shades later
As soon as the sun starts to set, whisk your curtains shut to hold in the heat. Warmth can escape through windows and doors, so invest in thick curtains to add as much insulation as you can. Place some in front of glass doors too to protect another vulnerable area.