I actually did not know the first part of this tip! I hadn’t really thought about it I guess 😛
Reduce the heat when cooking. Begin cooking on a higher heat setting until the liquid begins to boil. Then lower the temperature and simmer the food until fully cooked. A fast boil doesn’t cook faster than a slow boil (I hadn’t really thought about that!), but it does use more energy
Put a lid on it. Cook food and boil water in a covered container when possible. This traps the hear inside and requires less energy!