Not necessarily a Homesteading specific thing, but more of a how to live thing for those who want to reduce their electric bill, and can tolerate some temperature variation. There are a few requirements for this particular method to work out. The first is having a house that has windows that open, as well as having blinds. Preferably good thick blackout style curtains. Second is that the house is well enough insulated that heat transfer takes a good long time. If you've got wind whistling through cracks in your walls you're fairly close to stuck with the outside temperature plus or minus a few degrees. Third is paying attention to the weather. If you have all of these, you can get by without AC and still be comfortable.
How Does It Work?
The method I use to keep the house comfortable is fairly simple. If you are trying to keep the house cool during the day, you open the windows starting a bit after dusk when the air has started to cool significantly. You don't want to open the windows as soon as the sun goes down unless your house is already warmer than it is outside. When you open all of the windows make sure that as many air spaces in the house as you can are connected, meaning leave the doors cracked. If for some reason rooms can't do so during the night, leave them closed off during the day.
Leave the windows open all night long until just before dawn ideally. You can find what time dawn will be in your almanac, or an online weather service. If you can't get up at or before dawn, make sure that as soon as you get up you close every window in the house, and close all of the shades. While this means you aren't getting the nice natural light through out the day you will be keeping cool. Obviously this method doesn't work nearly as well in places like southern Texas where you're looking at 90 degree nights for part of the summer. In those cases in addition to opening the windows at night, fans move a lot of air.
If you are trying to retain heat, it's very easy. Close all of the windows at night, and leave the shades open during the day. This will probably make the house a touch too warm during the day, but if you have very cold nights can keep you from having to kick in the heat. Keeping the house warm works best if you have good south facing windows (north facing in the southern hemisphere).
Some Things That Make This Easier
* South facing windows
* Double pane insulated glass
* Good blinds
* Windows in every room of the house
* High efficiency fans
* A location that provides a good bit of air movement at ground level
Why Does This Work So Well For Us?
We have south facing windows, good blinds, double pane glass, heavy insulation, windows in every room, an opening, north facing skylight, a good bit of air movement on the hillside, and cool nights. New England is just about ideal for this kind of summer cooling, and our house doesn't even have air conditioning or even fans. Having lived in Texas in the summers for a good part of my life, I wouldn't enjoy this method there. That said, remember that much of the world lives without air conditioning at all and survives. They survive by using similar methods, construction designed to minimize sun beating on the living spaces of a house, and taking a nap during the hottest hours of the day.