Air conditioners are a luxury for most, and as they are a major strain on the grid, they must be used (if used at all) efficiently and effectively. One of the best things you can do is only run the AC if you are home, and awake. This can most easily be accomplished by getting a programmable air conditioner, that you can set to shut off automatically in the night and during the day when you are not home.
Take a quick look around your home. Are you skipping steps that could decrease the load on your taxed air conditioning system? Make sure that blinds are closed in the afternoon. Install awnings on the outside of the house. These are easy tasks that will greatly improve the temperature in your home, before the A/C is even turned on.
You can also assist the work of your air conditioner by using well-placed ceiling and floor fans to circulate air in your home more efficiently, and to create a cool breeze effect in your space.
Lastly, if your air conditioner is more than ten years old, consider replacing it with a newer, more eco-friendly model. Some newer A/C units can use up to 50% less electricity than older air conditioners.