You do the same thing when you leave your chimney flue open. An open flue lets out as much warm air as a 48-inch open window, the DOE says, so make sure the flue is closed when you're not using your fireplace. If you never build fires, consider closing up the fireplace. When cooking, use your microwave or toaster oven for smaller meals. They use much less energy than electric ranges.
Pressure cookers are also more energy-efficient because they reduce cooking time.
To prevent heat from escaping, use pans that match the size of the burners. Plant a tree. Or better yet, plant several trees. Deciduous trees planted on the south and west sides of your home will help keep your house cool in the summer and let the warming sun shine through the windows in the winter. Evergreen trees and shrubs on the north and west sides of your house will help deflect cold winter winds.