Remember when you learned about surface area vs. area in elementary school? My class did an "experiment" with sugar cubes, seeing which size dissolved first in the glass of water. To minimize cooking time, use the same principle - maximize the surface area.
For example, if you make mashed potatoes and you first boil the potatoes, it really doesn't matter how big you chop the potatoes, right? However, I see some recipes that call for boiling whole potatoes. That takes a lot of time! If you just take a few minutes to cut the potato into cubes, you can drastically cut down on the boiling, saving you on time and energy bill.
The same idea works with cake mixes. If you look on the back cover, you see that if you use a cupcake tin instead of a 9x12 pan, you can shave off a few minutes of your baking time. Ovens do require a lot of energy, whether you are on gas or electricity, so make cupcakes instead of cake next time!
So if you want to save a bit of energy, make flatter cookies instead of dense, thin crust pizzas as opposed to thick crust, use thin spaghetti pasta instead of penne, etc. Barbeque thinner cuts of meat instead of a huge steak. Squish down beef patties when making hamburgers. It may seem silly but in the long run it will save energy, and I think the Earth right now will appreciate any little bit of help it can get.
This image is from dkimages.