When the temperatures are expected to be high, consider keeping shades closed throughout the day. It is amazing the difference in heat gain when the sun is kept off the windows. I have blinds, thermal shades and exterior sun screens that we use on the hottest days to keep the solar gain to a minimum.
I have a digital indoor and outdoor thermometer that I use to determine when the outside temperature has dropped below the inside temperature. When the temperature outside has dropped in the evening, I have a large box fan that is tightly fitted in a back bedroom window that exhausts the hot interior air outside. This causes negative air pressure in the house, and when you open other windows in the home, you will get a nice cool breeze coming in.
I have built a simple thermostat to control this fan, (See a diagram and instructions here) so when the house temperature drops below 67 or so, the fan turns off automatically. Don't forget to remove the fan, close up the windows and shades in the morning to keep the air as cool as possible during the day.
We have also installed ceiling fans to keep the air moving, this helps make it much more comfortable, especially in bedrooms. In my home, I have small room air conditioners that keep an individual room cool. this is especially nice on very hot evenings when you can't cool the house with a fan because the outside air temperature it too high. If you keep the door closed these window units are a great choice.
If you have a central air conditioner, there are a few items you should consider to keep it running at peak efficiency.
These will help keep he attic spaces cool. Ideally the attic is the same temperature as the outside air. In the summer, I routinely enter attics that are as high at 145 degrees! Ventilation and insulation are both critical to keep this heat away from your living space. If your attic has less then 12 inches of insulation consider having more added. This will pay for itself in heating in winter and keep you much more comfortable in summer.
When re-roofing a home, consider using light colored coverings. They will reduce the heat from the sun. We always recommend silver coating un-coated torch down roofs. It will extend their life and help cool your home.
Use automatic thermostats with timers to control your cooling system. Be sure your air filters are clean, and your ductwork is tight, well insulated and free from leaks. We see leaking ductwork every day!
We recommend that you plant trees that will drop their leaves in winter on the south and west side of homes. This way you have shade in summer and the sun can naturally heat the home in winter. Remember to keep all plants trimmed away from the building.