1. Just add water.
Soak a t-shirt in the sink, wring it out, put it on and sit in a chair that lets air through to you in front of a fan.
2. Sweat it out.
Water vapor produced by sweating actually takes heat away from your body. The best thing to do is to put your sweaty self in the path of a cool breeze or fan.
3. Dress for the heat.
Wear natural fabrics (cotton, silk, linen) rather than artificial fibers.
Wear Light Colors: Darker colors will absorb the sun's rays and be warmer than light or white clothing, which reflects light and heat.
Cover Up: Covering up may actually keep you cooler, especially if the heat is low in humidity. By protecting your skin from the sun beating down, you'll also shade your skin. Be sure your clothing is natural fabrics, and loose.
4. Go downstairs.
Warm air is less dense than cooler air so it ends up layered on top of the downward moving cooler air. Make your way to the basement or lower level. It will be cooler there.
5. Keep the air flowing.
In the evening, open windows and use fans to create a cross-breeze, circulating cooler evening/night air through the rooms. As soon as the sun hits the building the next morning, close all windows and keep doors and windows closed throughout the day until it is cooler outside than it is inside. Leaving kitchen cabinets open all night helps too; if you leave them closed, they store the heat.
6. Turn off electrical heat sources.
Turn off the stove or other sources of heat. Turn off your lamps, as well as your computer when you're not using it. Turn off your TV.
7. Eat spicy food.
It's not a coincidence that many people in hotter regions of the world eat spicy food. Spicy (hot to the taste) food increases perspiration which cools the body as it evaporates. It also can cause an endorphin rush that is quite pleasant and might make you forget about the heat.
8. Think cool.
Read books about climbing Mount Everest, visiting Norway, or watch "Ice Age", or "The Day After Tomorrow". You might not be physically cooler, but if your mind envisions a cold environment, you might feel a bit cooler.
9. Sit still.
Do not try to fan yourself because it can make you hotter. Trying to move while feeling hot can make you feel hotter.
10. Cool as a cucumber!
Slice a thin piece of cold cucumber and stick it in the middle of your forehead! This feels fantastic on a hot day and works almost immediately!