Old trick--My grandmother hung a curtain between her back bedrooms and the rest of the house. Those rooms were kept cooler for sleeping, and saved energy. We've done the same between our "bonus room" and the rest of the house. The room was great when there were 6 of us living here, but now we really only use it on weekends. So the thermostat is set low, and the room is curtained off (cheaper than a door, and it lets the light through), saving us energy and money, too.
New trick--We've installed programmable thermostats, which enable us to control the temperatures in the different heating zones of our house. Upstairs is chilly, except for early morning wake up/shower time. Downstairs in wintertime requires a sweater or two, but on sunny days, the sunshine from our south facing windows provides a boost!
Between the new and the old ideas, we've definitely seen a difference in our oil bills this winter. And we've had a snowy, cold (for Connecticut) winter so far.
The front door needs to have the weather stripping replaced. It's on the "to do" list. That will help, too. And every little bit adds up......we save money and our footprint on this beautiful and amazing globe is lighter.