1. Wear light colored, breathable, loose fit clothing.
2. Know how hot it will be during your any planned activities.
3. Protect your skin from the sun with some sunscreen. (Minimum SPF 15)
4. Hydrate well before and during outside activities.
5. Limit caffeine or alcohol.
6. Avoid sitting in a hot car or garage.
7. Take frequent breaks during activity.
8. Plan activities around cooler times of the day.
9. Ask your doctor or pharmacist if your medications may be effected by the excessive heat.
10. Use misters or a wet rag for cooling down when possible.
See the video link also discussing signs and symptoms of heat exhaustion: