Stay in an air-conditioned environment if possible. Shopping malls offer relief if your home is not air-conditioned. Check on the elderly. They are especially susceptible to heat-related illness. Eliminate strenuous activity such as running, biking and lawn care work when it heats up.
Proteins are an example.
Increased metabolic heat increases water loss. These most likely occur during the summer months but can also occur in the spring and fall, especially if there is a prolonged power outage. Finally, remember that it's easy to keep your cool if you're prepared for it.