It's important to make sure the metal ends of the jumper cables do not touch each other or any metal surfaces on the car until they are connected to the correct battery terminals. This is more difficult than it sounds: Under the hood, most areas are metal. If two people are available to jump-start a car, one person can simply hold the ends of the jumper cables safely separated while the other person moves between the cars, making the proper connections. One person can jump-start a car, but it requires close attention.
The Do's and Don'ts of Jumpstarting a Car Knowing how to jumpstart a car is a skill all drivers should have. Always ground the circuit and connect the jumper cables to the proper terminals. The vehicle with the dead battery should be allowed to run for 30 minutes if possible. This will let the alternator fully charge the battery. Start the working vehicle and let it run for a few minutes. The more “dead” your battery is, the longer you may need to run the working vehicle. Attempt to start your vehicle. If it doesn’t start, continue running the working vehicle for a few more minutes. If your vehicle DOES start, don’t turn it off!
With the battery locations in mind, park the vehicle with the good battery close to the one with the dead battery, but leave yourself just enough room to walk between them. As you are hooking up the jumper cables, make sure the metal ends of the cables don't dangle into the engine compartment, where they could get caught on such moving parts as a belt or a fan, or on the outside of the car, where they could scratch the paint. Turn off the ignitions in both vehicles, set the parking brakes and make sure that the vehicles are in either 'Park' or 'Neutral,' depending on whether they have automatic or manual transmissions. Turn off all accessories, such as lights and radio. If the vehicles are parked in a safe area, turn off the hazard flashers, too. Clamp the other end of the positive jumper cable to the positive battery terminal in the booster car. Again, confirm that a plus sign is next to the battery terminal.
Connect the negative cable end to the negative battery terminal in the booster car. Now that the negative cable is connected to the battery terminal, you can attach the other end to an unpainted metal surface on the engine of the car with the dead battery.
If a labeled remote negative terminal is available, use it. Otherwise, find an unpainted bolt or bracket that is at least several inches away from the dead battery. This will provide a solid ground while further reducing the possibility of sparking. Make a final check to confirm that the jumper cables are not near any moving engine parts, and then start the booster car. Let it idle for several minutes to build up a sufficient charge to start the other car's dead battery. If the dead battery is new and was drained by the car lights being left on for an extended period of time, it will probably start quickly.
If it is an old battery or if the car sat without starting for a long time (more than a month), it may take longer for the battery to charge and start. It sometimes helps to rev the engine in the booster car a little to hurry the process along.