There are many elements that work together to create a perfect composition. One such element is called 'negative space'. Negative space is nothing but the empty space inside the picture that is not the subject. However, it is one of the most important thing to be considered while framing.
Negative space helps define your subject. It is a design element, which balances your image and makes it look intresting. It can appear anywhere in a picture. If the model is in the center of a picture, the negative space is on either sides of the model.
Learn to see negative space. This space keeps changing as your camera moves. Negative space is not fixed in the image. In some images, the negative space is small and somewhat insignificant, while in other, it features far more prominently in the design. Like in the image below, the negative space is on the right, and is quite prominent.
Art Directors use this space for adding text when the image is used in a layout. When working for a magazine or an ad agency, mostly, this space is predetermined in the layout. See an example of negative space in a beauty shot below.
Try and find negative space in your own photographs, as well as photos that you see in magazines. Even in cinematography, negative space plays a huge role. Identify them in movies and commercials. Once you have learnt how to play with this space, you will notice a major improvement in your compositions.