Dress for the weather.
This seems like a simple thing to say, but it can save quite a bit of money.
When you dress for the weather, you can turn your heater down or your air conditioner up. You can open the windows and not have anything turned on at all. That is my favorite scenario and it is the most cost-effective as well.
If you tend to get cold like I do, keep a light jacket or cardigan with you to throw on when you need it. On the flip side, if you get hot easily, layer your clothing so you can take something off if needed. I always take something with me when I go out to the movies or a restaurant in the summer. They always have the air on full blast it seems!
My downstairs is always cooler than the upstairs, so I leave a jacket down there in case I get chilled. It saves me a trip back upstairs to retrieve one later. My husband’s workplace is the same way, so he leaves one there at all times.