Wear lightweight, light-colored clothing. Light colors will reflect away some of the sun's energy. Drink plenty of water regularly and often. Your body needs water to keep cool. Drink plenty of fluids even if you do not feel thirsty.
Water is the safest liquid to drink during heat emergencies.
Avoid drinks with alcohol or caffiene in them. They can make you feel good briefly, but make the heat's effects on your body worse. This is especially true about beer, which actually dehydrates the body. Eat small meals and eat more often. Avoid foods that are high in protein, which increase metabolic heat.