If you're less interested in major projects, use the change of seasons to conduct a few simple energy-efficiency measures that cost you absolutely nothing:
Clean your refrigerator. Refrigerators use more energy than any other home appliance, but you can make yours more efficient by keeping it maintained. Vacuum the coils on the back, or on the bottom, of your fridge, and check its temperature. Put a standard food thermometer in a small glass of water on the middle shelf; the temperature should register 41°F, which is optimal for food safety but not too cold to waste electricity.
Clean your dryer. Lint can build up in your dryer's hose and in the pipes running to the dryer's external vent, increasing your dryer's energy use by up to 30 percent. That not only creates a fire hazard, but it also prevents moist air from venting outside, which can cause mildew problems, particularly in winter. Vacuum out the lint filter with your vacuum cleaner's hose attachment. Then detach the dryer hose from both the dryer and the wall, and vacuum lint from the back of the machine and from the pipes where the hose attaches to the wall. Finally, head outside to clear any linty obstructions from your dryer's external vent.
Open the drapes. Solar heat is the best kind of heat: free. In the summer, it's best to close the drapes during the day, to prevent heat from coming in, and then open them at night to allow the heat to escape. In the fall and winter, reverse that: Keep them open to let heat in during the day, and then close them at night to prevent it from escaping.