This is a list with some great tips for running and training in the summer heat. The source is the weekly newsletter of the Desert Road Runners, a running club based in Dubai and headed by the very knowledgeable Graham Michael Rafferty:

1. Slow down. In hot / humid conditions your body cannot lose heat as fast as in cooler conditions. If you slow down you will generate heat at a slower rate and be able to run further before your body overheats forcing you to stop.
2. Train according to time not distance. If you normally run for an hour at 5:00 / km pace you will cover 12km. In the summer you may find that you can only run 8 km at 5:00 / km pace = 40 minutes before you become exhausted. But if you slow down to 6:00 / km pace and can run for an hour then you will cover 10km.
3. Do interval training. The recoveries allow your body to cool down.
4. Drink according to thirst. Over hydration dilutes sodium levels in the body and is very dangerous. You will probably need to drink at the same frequency time-wise as you do in cooler conditions, but if you are running slower this will be at more frequent km intervals. Whilst it is important to remain hydrated, taking on water does not prevent heat exhaustion or heat stroke
5. Avoid running in the hot sun. Direct radiation from the sun heats up your body.Train early morning or at sun set.
6. Do not take any salt supplement. The salt content in your food intake is more than enough even in hot conditions. Your body regulates the amount of salt lost in urine and through sweat to maintain the level of sodium in your body at the correct concentration.
7. Carbohydrate supplements can be a boost during training.
8. Stop training when the effort becomes too great. This is natures way of telling you that your core body temperature is rising too high.
9. Use a heart rate monitor. Your heart rate will rise to 30 bpm higher than when running at the same pace in cooler conditions. Any more than this and you should stop training. You will get no further benefit from carrying on.
10. Try cycling. For less effort cyclists move faster and hence get more cooling effect from the breeze.
11. Train in a gym. But note that the ac in a gym may not be turned that low and there is no cooling effect from a breeze.
12. Weigh yourself regularly before and after training sessions.  I find that even though I am drinking frequently during a training session I still end up around 2kg lighter after a humid training session. That means I need to drink 2 litres of water to replace lost fluid. If muscles are dehydrated the risk of injury is much higher
13. Avoid the problem altogether. Train on the indoor track at the World Trade Centre Exhibition Halls. It’s free. Forget the distance, it’s not important. Just choose how long you want to run for and run to heart rate.