1. Drink plenty of water and take a good supply of drinking water with you in the car.
2. Make sure your oil and coolant levels are correct before you set off.
3. Do not leave children (or pets) in the car, even for short periods.
4. If you do get stuck in traffic, keep an eye on the temperature gauge for signs of overheating and, if necessary, find somewhere safe to pull over and let the car cool down for half an hour.
5. If it's not safe to pull over, turning on the heater may help take some heat off the engine (although it won't be very pleasant for you).
6. If you're likely to be stationary for a long time, switch off the engine to avoid overheating.