Putting jumper cables in your trunk doesn't mean you automatically know how to jump-start a car, but at least you did it before your battery died, right? But if you don't use jumper cables properly, you can fry your car ... or yourself. Though the procedure is really simple, you should learn how to do it before you actually need to. Not standing on the side of the highway while reading this article on your phone. That's dangerous.
Here's the stuff a step-by-step guide might leave out: First, get out of the way of traffic. Common sense (or self-preservation instinct) should tell you not to smoke. Less obvious, but otherwise logical, you should wear eye protection, make sure the two cars are parked so they're close but not touching and ensure no cables or connector ends touch anything other than the correct terminals. Don't keep cranking if it doesn't fire up -- just give it a little more time. And make sure the ignition is switched off in both cars before you start attaching cables. Even the dead one.