This is one of the most common chest exercise that does not require any exercise equipment and it works great. There are many variations of this exercise you can do to increase or decrease the difficulty and vary the effect on different sites on chest. These Exercises target both chest and triceps depending on the variation you are doing.

Figure Showing execution of a push up.

To do push up properly

• Place your palms on floor shoulder width apart.
• With Knees and back straight and parallel to floor lift off from the floor in slow and controlled fashion
• Now slowly lower your body and count as one
• Repeat this until failure.

Here are some excellent videos showing how to do push ups without getting injured.

You can also use push up stands for grip.