Begin on all fours with your shins and toes resting on the fitball
Now slowly lift your knees so your body is in a straight line from shoulders to toes, you may need to walk forward with your hands slightly
Now raise one leg off the ball
Slowly lower yourself towards the floor until your chest is a few inches from the floor
Now raise yourself again so your arms are almost straight
Repeat steps 4 and 5 until you can no longer maintain correct technique
Tips
For your first attempt of this exercise ask someone to hold the ball steady for you, if nobody is around then place the ball against a wall for stability - ONLY for your first attempt though!
Try to keep a straight back at all times
This is one of the hardest of the push ups so be sure you can manage at least 10 normal push ups before attempting this