If you've decided recently to start making some home improvements, especially to increase the energy efficiency of your home, you should investigate replacing your garage door or investing in some garage door insulation.
It's a key ingredient to the recipe of saving the planet and saving some cash. You can re do all of your windows and change light bulbs to the ones that save energy, but you may want to invest in something that will make a large impact and a long lasting one too. Plus, your garage is one of the largest rooms in your room. If you live in place that has freezing winters and burning hot summers, then you're probably leaking tons of energy keeping your garage at a good even temperature. If your door is unprotected, you're just bleeding money and energy.
You can buy several products you can obtain to do your garage door. There are many insulation products that will work. Most come in big fat rolls of sheets and can be applied like wall paper to the inside of your door. Some sort of foil layer is involve,d and a bubble layer, and a foam core layer. You can just cut the pieces to fit the door where you need it. The work of installing it shouldn't take very long at all.
Its a pretty simple measure, but you can almost halve the amount you're paying each month. It's a great idea. Your other options are to invest in a thicker or differently materialed garage door. Aluminum, for example, isn't very good for insulation in general.