1. Minimize the number of times you open the oven/refrigerator/freezer doors, or remove a lid from a pot.
2. Reduce cooking times by thawing frozen foods in the refrigerator beforehand.
3. Match the size of any pots or skillets you use on the stovetop elements. There’s no need to use the energy required to heat up the largest element when you’re only using the smallest pot in the kitchen.
4. Use a toaster oven or microwave instead of the stove oven whenever possible.
5. Optimize the use of a preheated oven by cooking several dishes, either at once, or in a row.
6. Keep appliances and pots/pans clean. The cleaner the surface, the more efficiently it can transmit heat (or lack thereof).
7. Don't turn on the oven too soon before you need it. Just a few minutes may be all that's necessary for pre-heating. Turn off the oven or stovetop a few minutes early. The residual heat will keep cooking the food.
8. Cook several meals at once. You'll skip lots of energy wasted when stuff heats up and cools down. If you're ambitious, do once-a-month cooking.
9. Use a Pressure Cooker. It uses less energy than standard cooking.
10. Don't put warm food in the refrigerator. It takes extra energy to cool it. Let it sit out and cool to room temperature, then put it in the fridge.
11. Use a cover when boiling water. It'll boil faster that way.
How to Reduce Energy Use While Cooking from wikiHow