Those without A/C, what are your tips to stay cool during the summer?

I used to not have AC. I found the best strategy was to open up all the windows at night and let the cool night air in, and then as soon as I wake up I close all the windows, curtains and blinds to trap the cool air in and prevent the sun from heating it up through the windows. If you live in a house that has a basement and central heating, you could add some intake ducts down there and turn your furnace on to fan only mode to circulate the cool basement air into the rest of the house.