Make sure you know what the rating is for the unit you are considering buying. A window air conditioning unit should have an EER of 8.0 to 12.0 to be considered efficient, and the higher the number, the better. Replacing or cleaning a dirty air filter is probably the simplest maintenance job there is. Air filters don't just keep the air fresh, they save you money on your energy purchases by making it easier for the system to work and improving the system's performance. Clean filters also prolong the useful life of your cooling equipment by keeping dirt and dust off diffusers and coils and out of fans and motors.
Most air filters are disposable, although an electrostatic filter can be cleaned with water.
Either way, air filters should be replaced or cleaned monthly. Regularly turn off lights that are not being used. Use fluorescent lighting as it is more economical than incandescent lighting, and produces five times more light with the same amount of energy and lasts 10 to 15 times longer. Purchase lamps with three-way switches, as you can lower the settings when less light is required. Install dimmers for lighting control.