How to Prepare for Running in High Temps

August is typically the hottest month of the year in the Mid Atlantic region.  This type of heat has a direct impact on how you should train.  You should never just rush out into the heat and run a quick 5 or you might become dehydrated and harm your body permanently.   Work with your doctor to figure out what is best for your situation and never take risks when you don't need to.  I've been training for a marathon that I plan to run in the fall.  Unfortunately, dealing with the heat in the DC area is just a fact of life, but training in it is like being pregnant in this hot climate--there are good days and bad days.  I usually run after work during the week, so the temperatures usually averages between 85 to 95 degrees with 40-70% humidity.  To handle such heat and humidity, I've tried to acclimate myself to the heat over time.  It doesn't happen overnight.  It takes weeks of training.  I usually never run distances over 10 miles in such heat. and I average 5-7 miles a day during the week, and run my long run on the weekend early in the morning.  Now that I'm acclimated to the heat, it doesn't hit me as hard, but I always take precautions.   Below are a few tips to consider that may help you cope with the heat.
General Tips:
1.  Make sure you are sufficiently hydrating before, during and after run. 
2.  If you run distances greater that 5 miles or 45 minutes, make sure you drink water and a sports drink with electrolytes during the run and sufficiently hydrate the night before the run. I prefer GU Brew and water.
3.  Run with a wing man, especially if you are running long distances.  This way if you are feeling poorly at least you have safety in numbers.
4.  Where appropriate clothing.  Try do avoid dark clothing.  Wicking material is the best.  I like running without a shirt, but not always.  Socks that don't get as water logged are always nice.  Drymax work pretty well.
5.  Where a hydration belt on long runs.  If I run 10 miles, I will carry a 16 oz hand held water bottle (filled with water).  I will also where a belt with two 8 oz bottles with GU brew.  If my runs are 10+ miles, I will carry a 16 oz hand held water bottle (filled with water).  I will also wear my belt with 2 8 oz bottles of water and 2 8oz bottles of GU brew. 
6.  Chew gum to keep your mouth moist.
7.  Take supplements for fuel and hydration.  I like GU Roctane.   I usually take one 30 minutes into run and then at the 1 hour and 30 minute and 2 hour and 15 minute marks.
8.  Weigh yourself before and after to determine appropriate water in take required.