Modern cars are significantly less prone to overheating than older vehicles, but it can still happen and you should be prepared in case it does. Most often, an engine will overheat when the weather turns hot. Low coolant levels can also cause this issue, so be sure to keep an eye on the fluid to prevent overheating.
If your car begins to overheat in hot weather, the first thing you can do is shut off the air conditioner and open the windows. This reduces the amount of work the engine needs to do. If this is ineffective, the next step can be to crank the heater and turn the fans on high. This removes the heat from the engine, and being sweaty and uncomfortable in a running car is a far better option than breaking down on the side of the highway or in the middle of stop-and-go traffic.
When your engine's temperature climbs and you are stuck in traffic, it is also important to go easy on the brakes. Many drivers will step on the gas and then jam the brakes when they are able to move forward, even if it's only a few car lengths of distance. However, an overheating engine will only be worsened by this behavior, as the constant acceleration and deceleration create more work for the motor. Instead, you should take your foot off the brake pedal only when you absolutely need to move and coast on the idling power of the engine.
When you are stopped, put the transmission in park or neutral and rev the engine. This speeds up the fan and the water pump, which can help cool the engine by pulling more water and air through the radiator.
If your engine is reaching dangerous temperatures and none of the above techniques are having a noticeable effect, you should pull off the road immediately and shut off the motor. Ideally, you should have the car towed to a location where it can be worked on, as driving it risks causing damage to the engine. Overheating can lead to a blown or cracked head gasket, which is typically expensive to repair.
When you're waiting for the engine to cool down, you can speed things up by popping the hood. Do not go near the radiator cap until you've waited a significant amount of time for the engine to cool. The cap itself can be very hot, and the coolant and steam built up inside the radiator may cause serious burns.