Do you drive these modern cars that won't push start on flat battery; cars with electronic pumps (no power, no fuel) or even automatics (no clutch to play with)?
An older car may get away from this flat battery troubles when pushed on a safe runway. But sometimes this may not work which may result in you giving up.

A jump start can go a long way in getting you out of this trouble, but you have to be careful.
Be warned that jump starting your car should be the last thing you do when you must have tried out other ways to make your car come back to life. This is so to prevent damaging the electronic components of your car.

You can jump start using a booster battery or another car and these precautions must be taken.

Ensure all electrical equipment is switched off - wiper, light, heater
Ensure the booster battery is the same voltage with that of the discharged battery in your car
Ensure that the cars are out of gear; in automatic cars, the gear lever should be on neutral N or park P.
The two cars must not touch each other.

JUMP STARTING YOUR CAR
1. Connect one end of the red jump lead to the positive (+) terminal of the flat battery.
2. Connect the other end of the red lead to the positive(+) terminal of the booster battery.

3. Connect one end of the negative jump lead to the negative (-) of the booster battery.
4. Connect the other end of the negative (-) jump lead to a bolt or bracket on the engine block, well away from the battery, on the vehicle to be started.

CAUTION:
1. Ensure the jump leads will not come into contact with the fan, drive belts, or other moving parts of the engine.
2. Start the 'donor car', then start the engine of your own car. With the engine running at idle speed, disconnect the jump leads in REVERSE ORDER OF CONNECTION

SOURCE: http://emekaani..com/2015/02/jump-starting-car.html