Although it makes some sense to rev the engine of the donor car (more revs = more power = more electricity, right?), in actuality it does very little to help starting the recipient car.

Basically the alternator of the donor car cannot provide near enough current (about 65 amps on average, over 3000 RPM) for the short period of time required to start the other car. The donor car's battery therefore is needed to do the majority of the work (hundreds of amps of current are needed over a second or two). The donor car should running to allow the recipient car's battery to charge up a little before trying to start.

If the first try is not successful, simply wait a minute or two for the donor car's alternator to charge the recipient battery a little, then try again. Repeat until started, or bored.

I would recommend detaching the jumper cables as soon as possible after starting the recipient car to avoid a fire hazard. Once the car is started, one should drive it for a while (ideally 15 minutes or more after warming up) to allow the charging system to bring the battery up to a reasonable level so it will start again the next time.

Lastly, do not rev the engine of the recipient car until it has had a chance to warm up. The majority of the wear on a car's engine is in the first few moments of start-up when there is little or no oil on most of the moving parts. So revving the formerly dead car immediately after starting may be satisfying, but will do much more damage than any other start-up and could cause more problems later on.
Source(s):
http://www.bcae1.com/charging.htm
http://www.bcae1.com/

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