Growing up in Wisconsin and New Jersey, my family homes always had a fireplace. They were perfect for cold winter nights, for "indoors camping" or just for sitting near and watching TV. There's very little like the crackle and heat of an open fire.
That said, while your fireplace may be decorative, enjoyable, even functional, it's also one other thing: a great big hole going to the outdoors.
Many families have glass doors across their fireplaces. That's a good start, but there's something else you should remember to do, and that is keep the chimney closed. It's more than just a good idea; hot air rises, after all, and the money you spend heating your home could literally be going up the chute. You don't want Santa's doorway being a money-Grinch, do you?
Here's what you do. Clean out your chimney early. Burning wood leaves deposits of soot and creosote in the chimney flue; these deposits, accumulating over time, can catch and result in a household fire. For safety, a chimney should be inspected and even cleaned annually.
Once you do that, keep the flue lever turned so that the chimney is closed when it is not in use. A glass door may help prevent some heated air escaping, but it can't do the job by itself.
So enjoy your fireplace as we head into the winter months, but be safe and efficient while you do. You can find other no-cost and low-cost tips to save money this winter (and keep your fireplace efficient) at EnergySavers.gov.