1. Keep blinds and drapes closed when the sun is near or on windows.
2. Open doors and windows when the air outside is cool; for example, in the early morning or evening.*
3. Cook outdoors, or use methods of cooking that keep the kitchen cool, such as crock pot cooking.
4. If you have a dryer in the house, try line drying clothes, instead. (Don't have a place for an outdoor clothes line? Check out "Air Drying Laundry Indoors.") If air drying clothes just isn't possible, use the dryer only in the early morning or late evening, when temperatures are cooler outdoors and in.
5. At night, or when working in a single location, use a fan. On it's low setting, with just a light breeze being made by it, it can make you feel considerably cooler.
6. At night, place fans near open windows to help draw cool air in.*
7. Make your own swamp cooler. Place a metal bowl filled with salted ice in front of a fan that's blowing over the ice.
8. Turn on your stove fan and open your chimney flue. This draws hot air out of the house. (Some stove fans are heat-generating; obviously, if this is the case in your house, try to leave the fan off.)
9. Keep lights, computers, televisions, and other heat-generating appliances off.
10. Use satin or silk bedsheets. They feel cooler on the skin.
11. Close off the hottest parts of your house. For example, if you have bonus rooms upstairs, they likely get very hot. Close them off and don't use them during the hottest months of the year.
12. Install inexpensive heat-reflecting film on windows.
13. Use light-colored roofing materials. Approximately 30% of the heat that enters your house comes from the roof, and having a dark colored roof only intensifies this.
14. Get mini-blinds; they will make your house feel about 50% cooler.
15. Install overhead fans, which can make rooms feel up to 7 degrees cooler.
16. Add awnings to the outside of your windows. According to the U.S. Department of energy, this can reduce heat felt in your house by 77%.
17. Plant shade trees near the house (but not so near their roots will destroy your home's foundation).
18. Don't use rock, asphalt, or cement on the west or south sides of the house. Unless it's shaded, it will only increase the heat - indoors and out.
19. Weatherize and insulate your house.
20. Consider making your own $15 - 20 "air conditioner." Here's one example; YouTube is full of instructional videos for variations on this technique.
And if You DO Turn on the Air Conditioner:
1. Do all of the above, anyway. You'll appreciate it when you get your electric bill.
2. Make sure it's the right size. An AC unit that's too small for the room won't be very effective. Learn more about AC units and room size here.
3. Clean the AC air filter at least once a month.
4. Shade the outside of your AC unit; this can make the air coming into your house 10% cooler. (Just don't block the air flow of the AC unit.)
5. Make sure appliances and lights that generate heat aren't near your AC's thermometer.
6. Make sure plants and trees are at least 3 - 4 feet away from your AC unit, to encourage good air flow.
7. Consider installing AC only in rooms where it is really needed. It's unlikely you need air conditioning in every room of the house. However, if you just can't sleep when it's hot, it makes sense to install air conditioning in your bedroom.
* Consider safety, too. Open windows can be an invitation to criminals. Use your best judgement.