For your own safety, don't smoke; wear metal rings or watches etc. Don't wear loose clothing which could get caught in moving parts also keep hands well away from pulleys, belts and electric fans etc.
1. If possible check for specific procedures listed in the vehicle handbook and follow them, if this is not available follow this safe procedure.
2. Before connecting leads check that the batteries are the same voltage and ignition switches are turned off. Warning! If broken down vehicle is fitted with an electric hand brake it may release when connecting leads, either keep foot brake depressed or chock wheels.
3. Park the working vehicle as close as possible to broken down vehicle but don't let them touch. First connect the red lead to the positive (+) terminal on the flat battery and to the positive (+) on the good battery. Then connect the black lead to the negative (-) terminal on the good battery and to a suitable earthing point on the engine or chassis on the vehicle with the flat battery. With leads connected wait a few minutes for the batteries to equalize then start the engine of vehicle with the good battery and run at fast idle for a few minutes.
Now start the vehicle with flat battery and run at fast idle for 10-15 minutes. Warning don't remove jump leads with engines running as you could get a voltage surge and blow an electronic component.
Turn off both engines and disconnect jump leads in reverse order, try to restart vehicle with flat battery using its own power, if it does not start you may have a faulty battery/charging system.
If you believe that you have a faulty battery and want to drive to the garage for replacement it is possible to remove leads without damage, but you must switch on some load (heated rear window, heater blower, sidelights, headlights if not electronic etc.) this will absorb the electrical surge from the alternator when the good battery is disconnected.