With your arms extended and more than shoulder-width apart, lean up against a crossbar at mid chest level. You should be at a 45 degree angle roughly. This is your starting position.
Lower yourself down to the bar until your chest almost touches it. Then, push and raise your body up again to the original starting position. Repeat this movement for the desired or prescribed number of repetitions.
Perform this exercise in a smooth and fluid motion
Don't lock out your arms at the top of the movement
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement.
This is a good warm-up exercise. If you are on a mass-building cycle this will not do much for you because it's simply not challenging enough (if you are a guy). For women, this is a great exercise that can help tone and tighten the upper body muscles and is very comfortable to execute. Some women do this exercise modified by executing the movement on the floor with their knees down on the floor and legs crossed at the ankles.
As a warm-up exercise for guys this exercise is perfect because it gets your blood flowing into the chest muscles at an accelerated rate and will have the effect of priming your muscles before you engage in lifting weights and doing exercises for the chest.