Before you install a new air conditioning system, consider your home's electrical system. It's not uncommon for old houses to have only 110-volt, 60-amp service for the entire home, barely enough power to handle the home's existing complement of lights and appliances. Central air conditioners require a dedicated 230-volt circuit and may require 20 to 50 amps of power, making an electrical service upgrade necessary. Have an electrician size your home's electrical supply up before your HVAC contractor begins work.
Decorate with pale colors on walls, ceilings and floors. Soft tones reflect more light, so you can use lower wattage bulbs and delay turning on lights until later in the day. Using high-gloss paint can help as well.