Have your air conditioning unit inspected annually. They need to be periodically cleaned and tuned. Have a professional inspect and tune your system. Have them check the coolant charge, airflow, and the insulation on the cooling lines.
Keep rooms closed off and vents shut in rooms that are not used frequently.
Be sure your ducts are properly sealed and insulated. Duct leaks can allow cool air into your attic or crawl space or they can draw hot air and moisture into your home.
Install a timed thermostat that turns on the AC later in the day and off earlier in the evening when it is cooler.
Use fans to keep the cool air circulating thoughout your house.
Dark colored roofing absorbs a lot of solar energy, which is converted to heat in your attic and living space. The next time you re-roof your home, consider installing white or other light-colored shingles to reflect more solar heat.
When solar energy heats your attic, this heat radiates through the ceiling and heats the rooms below. Attic insulation slows this heat flow, and it also slows the heat flow out of your home in the winter. Add attic insulation to total 16 inches or more if you currently have less than 6 inches of insulation.
Windows allow sunlight to pour into your home. Awnings, sunscreens, or curtains over the windows that receive the most sun will help keep the heat out.
Obstructions surrounding the outdoor unit of your air conditioner will reduce the airflow over the condenser coil and lower the efficiency of your system. Be sure to remove any leaves, branches or debris from the outdoor unit to keep the air around the unit circulating freely.