Before firing up the engine of the working car, it's important to attach your jump leads in the correct order:
1. Red cable to the positive terminal on the dead car battery.
2. Red cable to the positive terminal on the working car battery.
3. Black cable to the negative terminal on the working car battery.
4. Black cable to a bare metal surface on the car with the dead battery.
When it comes to disconnecting the jump leads, simply do this in the reverse order.