1. Run in the early morning. If you need to do a longer run and don't have enough time, do part of your run in the morning and finish it up in the early evening when it's cooler again. Not ideal, but better than just a short run or no run at all.
2. Find an alternate route that provides more shade or hit the trails which usually provide more protection from the sun.
3. In addition to hydrating well before your run, make sure you carry water or your favorite sports drink with you on the run by either wearing a hydration belt with one or more bottles, carrying a handheld bottle, or a hydration pack. If you don't like wearing a belt, pack or using a handheld bottle, be sure to place some water/sports drink along your route. Just be sure to go back and collect any empties.
4. Splash it on! Fill one of the bottles on you hydration belt with water. Not to drink, but to pour on your head during your run. Regularly pouring a little water on your head/body during your run can help to increase the evaporation-cooling effect.
5. Don't wear cotton! Be sure to wear tops and bottoms made of lightweight technical fabrics designed to whisk away moisture keeping you cooler and dryer. A water-logged cotton T-shirt can actually slow down the evaporation-cooling process causing you to overheat.
6. Wear a visor or a hat with a bill. This will provide shade for your eyes/face as well as help to keep the sweat rolling off your head from getting in your eyes. Make sure to use a hat appropriate for the heat that's made of lightweight technical fabric that will promote evaporation.
7. American Running & Fitness Association recommends that you "acclimatize" yourself to the heat. To do this on your first run in the heat, you should cut your intensity by 65% to 75%. Then over the next 10 days, slowly build back to your previous level.
8. Refrain from being too competitive with your buddies on your regular runs. Save it for the weekend races.
9. Don't run alone. Having a buddy on a run is good because you can each look out for the other for any signs of heat exhaustion or heat stroke. If you do have to run alone, be sure to let someone know exactly where you'll be running and approximately how long you'll be gone so, if something does happen and you don't return, they'll be able to search for and find your quickly.
10. Check out air quality index rating before running. If it's a code orange and you're sensitive to air pollution and/or have upper respiratory problems you may not want to run. If it's a code red, it's not suitable for anyone to run. Check the weather section of your local TV station's website. It will usually provide such information.
For even more tips on running in the heat, check out this great video clip from Howcast.