Why? When performing a push-up, most people either sag their hips, stick their buttocks in the air or drop their head towards the ground. This reduces the effectiveness of the chest workout and is bad for your spine.
How? Start with your hands shoulder-width apart, resting either on your toes or knees. Your body should be in perfect alignment throughout. At the end of the movement your nose, chest and hips should all be centimetres from the ground. Squeeze your pecs together as you push up to increase your chest engagement.
Sets and reps: 2 sets of 8 to 15.