Basic things you can do:
1. Know the heat exhaustion/stroke symptoms: nausea, rapid heartbeat, confusion, disorientation, dizziness, muscle cramps, lack of sweating (even though you ought to be sweating).
2. Wear loose clothing, and wide-brimmed hats.
3. Drink water, tea, Gatorade. Squeeze a bit of lime or lemon into a glass of water. Don’t drink alcohol drinks.
4. Do physical stuff in the mornings, and avoid afternoon sun.
5. If you got any medical conditions, that just doubles up your risk in high-temp situations. Stay in the shade when possible.
6. Cold watermelon is a good afternoon treat.
7. Keep a bottle of water around and sip it every 30 to 60 minutes.
8. Walking out to the car at noon? Open the doors and let it air out a minute before you jump in.
9. If you have to be in the sun for an hour...use suntan lotion and a loose long sleeve shirt.
10. If you think for a moment that you got symptoms of heat exhaustion/stroke...stop and let someone know. Find shade, and sip as much water as you can.
11. Take sea salt tabs. 450 milligrams for every 25 pounds of body weight, once per day.
Doing so, will mitigate all of the heat related symptoms, such as cold chills, dizziness, muscle cramps, headache, exhaustion, nausea, etc.
I've worked outdoors doing construction in the southwest for decades, and can attest that this works. Just make sure it's sea salt, and not regular ionized salt, which helps, but isnt nearly as effective.
I’ve never understood the “sipping” part. Working in the heat (110 + sometimes) I’ll drink 10-15 bottles of water and gateraide. I alternate them, and drink at least one bottle on the drive to the site. I see the bottles are 16.9 ounces. Recommended normal drinking is 8 to 10 glasses (8 ounces) a day. Of course if I’m sitting at my desk I’m thinking “How the heck can I drink eight glasses of water!?”