There are some easy, free, or cheap steps in winterizing your home while the weather is still warm. One is cleaning out your gutters and eaves to allow melting snow to get away from your home. A clogged eave can allow melting snow to dam up and run down the wall of your home.
If you have ceiling fans, there is a switch to change the motion of the blades to move in a clockwise direction. This allows the warm upper air to push down to the floor.
If you have the older single-pane windows, you can get insulation film for the inside of the window. This will keep up the top 60% of the inside heat from leaking out. Using heavy curtains also helps. One of the best things I did was to replace the old windows and storm windows you a to put on every fall with double-pane energy efficient windows.
If your windows leak around the outside edges, use rolled weatherstripping putty to seal the warm air from leaking outside. Any remaining gaps around the door or windows can be filled with caulk. If the home is older, you can pull off the moldings and fill the gaps with insulation or caulk.
Draft guards are a good idea if you have a small exterior gap. These guards are placed under the door and will slide with opening and closing.
Replace your furnace filters to keep your furnace running efficiently. Using a programmable thermostat or one use can use on your phone greatly helps. You can turn down the heat when you are not there and turn it up before you get home. Department of Energy states you save 1% for every degree you lower on your bill.
If your water heater pipes are in a cooler area like a basement, get pre-slit pipe insulators or batt-style wrap for your hot water pipes.
If you have a fireplace, check it for obstructions and soot. There is a new product on the market, the chimney balloon use to run up your chimney.
If you are doing major upgrades like installing new windows or furnace, there may be federal tax credits so check with your accountant.