I have been trying some of his tips, plus some of my own ideas, and thought I'd share them here.
The results have been very successful, and at my house we now run our air conditioner for only brief periods of time throughout the day while the other tenants in our unit blast theirs almost nonstop.
The most interesting thing I discovered is just how arbitrary the standard 72 degrees F is. I am convinced that this temperature is based on wearing a business suit, which people almost never wear in their own homes in the summer. The truth is that there is no ideal temperature.
These ways to stay cool fit into three categories: Lowering the temperature of your house, lowering your body temperature, and changing your perception so that the heat doesn't bother you so much. Not all of these steps are practical for everyone, but if you can find one or two that you can turn into habit, it can make a difference in comfort and/or in energy consumption.
In addition, I have listed some bonus "green" benefits on each step where they apply.
Step 1: Get Naked!
I know this isn't for everyone, but its amazing how much more comfortable 80 degrees Fahrenheit feels if you're shirtless.
If you live on your own then this is no problem.
If you live with close friends or family, then wearing just your underwear is probably not a big deal either.
If you live with roommates, you can wear lighter-weight clothing like shorts, tank tops, etc. Even going barefoot helps your body eliminate heat more effectively.
In any case, you can probably wear as little clothing as you like at nighttime while you're in bed. If it feels strange at first, give it a few nights and see if you don't get used to it. While you're at it, get rid of your blanket and just sleep under a top sheet.
Wear fabrics like jersey cotton, nylon mesh or linen which don't hold onto heat.
BONUS: You will end up doing less laundry.
BONUS: Your clothes will last longer since you are spending less time wearing them and not washing them as often.
BONUS: Being naked is fun.
Step 2: Get Wet
Take a short (5-10min.), cold shower whenever you feel too hot. It lowers your core temperature which means you'll stay cool long after you get out of the shower. This is great when you come home after work and first walk into the house. Plus you'll be undressing anyway (see step 1) so why not cool off a bit more while you're at it?
This is also great right before you go to sleep since the body must lower its temperature before you can fall asleep at night. I fall asleep much faster this way in the summer.
If you don't like the shock of stepping under cold water, you can try a cool shower (which works just as well but takes a little more time) or you can start off with a moderate temperature and slowly reduce it every minute or so. This has its own relaxing quality, much like if you were slowly raising the temperature.
Make sure to get your hair wet; that will keep you cool even longer.
If you are following step one and do not need to put on a bunch of clothes, then there's no need to dry off. The water on your skin will act like sweat and carry away your body heat as it evaporates.
BONUS: A cold shower uses less electricity than a hot shower. Saves money & carbon emissions!
BONUS: Your house will not get full of hot steam, which raises the temperature.
BONUS: If you like long showers, you won't use up all of the hot water no matter how long your shower is.
EDIT: Several people have suggested getting your clothes wet and then putting them on to stay cool. I don't do this because I don't like having heavy clothes hanging off of me, slowly me down, getting my furniture wet. But if you don't mind these things, then go for it. It will indeed keep you very cool.
Step 3: Get Hydrated
Keep a jar or pitcher of tap water in your fridge and sip it throughout the day. The water will absorb your body's heat as it gets absorbed by your stomach.
Even drinking tepid water will help keep you cool, since being fully hydrated makes it much easier for your body to thermoregulate.
Some people don't like drinking water. Try making some sweet tea or herbal iced tea. You can steep tea iced tea while its in the fridge if you do it for several hours. Sweetened drinks, though not as effective as water, will help keep you hydrated too.
BONUS: Being hydrated improves performance and concentration, prevents fatigue and headaches, and controls hunger.
BONUS: Choosing tap water over bottled water conserves additional money and natural resources. Most tap water is as clean as or cleaner than most bottled water.
Step 4: Fans!
Fans are much cheaper to run than most A/C units and moving air feels cooler even when it isn't. This is because it blows your body heat away as soon as the heat exits the body. It also helps to evaporate any sweat that might be on your skin or any dampness still in your hair from your cold shower, which will cool you through evaporative cooling
If the outside temp is cooler than the inside temp, you can position a fan in your window to bring in air from the outside.
To take it a step further, place a fan in the window on each side of the house, but point one fan toward the outside so that it is sucking air out of the room. This will create an air current through the entire house. If you have two floors, put the "outside" fan upstairs and the "inside" fan downstairs or in the basement. This is similar in principle to a whole house fan.
Finally, make a paper fan or a cardboard fan. Get in the habit of fanning yourself while you're just sitting watching TV or browsing instructables.
BONUS: You can make funny voices by speaking into your fan!
Step 5: Windows
Speaking of windows, open them! Keep them open all night and then close them as soon as the outside temp exceeds the inside temp. In the evening, when your house has heated up, open them again.
If the sun is shining in your windows, close your blinds or shades but leave your windows open.
Step 6: Home Improvements
-Paint your house white. If your house is cinderblock or brick this can make a difference since white reflects more heat than darker colors.
As we saw earlier, you can install a whole house fan.
-Get some shades above your windows and blinds that will let in air but not light. This way the sun won't shine into your room making it warmer. Plus you can have the windows open without the neighbors seeing you walk around in your briefs.
-Plant trees near your house, especially by windows. This is yet another layer of protection from the suns rays.
BONUS: Some home improvements, such as improving your insulation or installing heat-reflecting roof tiles make you eligible for tax deductions.
Step 7: Turn Off the Lights.
In the daytime there should be plenty of light coming into the house through the windows. Light bulbs not only emit heat; they also make it seem warmer.
This means that, believe it or not, turning off lights will make it seem cooler. Try it and see if it works for you.
BONUS: Less electricity spent on lighting.
Step 8: Turn Off Everything Else.
All of these appliances emit heat, which you're trying to get rid of. If you don't use them, you won't have them dumping more heat into your house.
With your fan on, you can hang up your wet clothes inside the house instead of outside. As the fan circulates air through your wet clothes, it will cool the air through evaporative cooling. Your clothes get dry, and your house gets cooler. Win-win! (Note that this works much better in dry climates than in humid climates.) Thanks to javandyck for this tip!
BONUS: It will save even more electricity, money, and carbon emissions.
Step 9: Speaking of Perception...
Your skin is covered in thermoreceptors, and those are the only thermometers that matter. When you feel hot, turn up the fan, take a cold shower or, if needed, turn on the A/C for a little while. But thermostats and thermometers breed discontent. You might be feeling perfectly comfortable but see that its 80 degrees in your house and it will convince you that you're supposed to feel hot. So of course, you will start to feel hot. If you have a thermostat that insists on displaying the temperature, cover it with a piece of tape.
This is a silly little trick, but its also easy to do and works very well for most people.
Step 10: Just Be Cool
Another thing to remember is that if its summertime, its okay to feel hot. Isn't that what we spend all winter wishing for? Let it be summertime and be a bit warmer. Eat some melon. Take a nap. Swim. Go to a BBQ. Its supposed to be warm!
Humans have lived in every climate for thousands of years. When did we get so fragile that we had to always be at a constant temperature of 72 degrees? Who came up with that number anyway?
Well that's the end of my rant and my instructable. Just remember that its okay to feel hot when its hot.
See you at the swimmin' hole!