Depending on where you live and the climate you may have substantial heating bills in the winter. Even if you heat with wood, you either need to buy it or spend lots of time and effort otherwise procuring it.
The first place to look is windows and doors and any cracks they may have. Feel for air moving though. Weather stripping is cheap, easy to install and effective and can help here a lot. Sometimes replacing the entire windows is something to consider as new better insulated windows may pay for themselves in a few years due to heating cost savings.
Solar is an option, and the easiest way to use solar is simply to open the shades and curtain when it’s sunny and let the sun and warmth in. Even unheated rooms will sometimes be warm midwinter from the sun.
Look at insulation too. Some older homes may not be insulated well. It’s even possible to have insulation blown into some types of walls.
Also, are you heating your whole house? This may not be necessary at all. We close off several rooms in the winter, and only heat them when we are going to use them. This alone accounts for lots of savings.
Of course you can also look at alternative heating sources. There are federal credits for many types of green technologies like heating you may look at, wood may be something to consider if you have a lot around as we do, and geothermal may be a possibility as well.