When attaching the clamps to the batteries try not to ‘tap’ them on and off, make a solid connection and leave it there, otherwise you can cause damage to the electrical system and in some extreme cases; battery explosion.
If you are not 100% sure of what you are doing, seek professional help.
1 - Make sure all electrical accessories (A/C, stereo, lights etc) are switched off within both vehicles, and turn off the ignition.
2 - Attach the red cable to the positive (+) terminal on both batteries.
3 - Attach the black cable to the negative (-) terminal on both batteries.
4 - Make sure all connections are secure.
5 - Start the engine of the 'donor' vehicle and let it run for a minute or two whilst slightly pressing the accelerator pedal to raise the idle speed, during this time the dead battery will begin to charge.
6 - Attempt to start the 'dead' vehicle; if the connections are secure then there should be enough power to get it started, as long as there are no other problems.
7 – Leave both engines running for a few minutes
7 - Disconnect the black cables from both batteries first, then the red.
8 - Leave the engine running to allow the alternator to continue charging the battery. If there is a red battery warning light on your instrument panel then there is a problem with the charging system which means that the battery will very quickly discharge again, the vehicle should be recovered to a garage to be professionally diagnosed and repaired.
Note - there has to be a cause of a battery discharging, this could be lights left on, faulty charging system, a current drain whilst the vehicle is off, or maybe just a worn out battery. Make sure you find the cause or you could well find yourself in the same predicament.