Hmmm hard question to answer accurately. Depends “who” you are. Producing enough food for people in the world takes a lot of energy. If we ate locally produced and seasonal food we would save a lot of energy and carbon – also eating less meat (because cows FART a lot a produce methane). Taking the bike to work instead of the car is a good one for me – saves up to 225g of carbon for each km). Buildings in the world use up about half of our energy, so turning the thermostat down in your house by just 1°C could save about 500kg of carbon each year….
hope this is helpful – there are lots of ways to save the world..