Why divide a picture to three and how will it affect our photography skills

The “thirds” are no more than imaginary crossing lines that divide the image into three vertical sections, and three horizontal ones – Nine sections in total. 
 
Notice how the central objects in the following photos are located more or less at the corners of the central square (e.g. One third of the way from top to bottom and right to left).
    
If you take a picture with the use autofocus, shift the camera right or left, up or down, so that the object will be located at one of these imaginary intersection lines (These lines will not appear on your camera as they are imaginary, so it’s not critical whether you place the object exactly at the point of intersection or anywhere near that point).

How to use the thirds in  portrait pictures 

In most cases, the main object in a portrait will cover a large part of the photo. In this case, it is customary to choose a central part in the face of the object and place it at one of the intersection thirds.  The nearest eye, for example, or bulging lips – can act as a good center to be shift at one of the intersection points.

The rule of thirds and photography of motion

The rule of thirds also refers to objects in motion. In this case, it is important to distinguish the object’s direction of movement:  If, for example, you shoot a car going from right to left, place the car at the right third of the image, and thereby allow the viewer to see "where the car was going". This, of course, is true in most cases. On the other hand, you may wish to emphasize the car’s route or the trails it leaves behind - but usually it is costume to see the object as if it was on the move. The same applies if, for example, you wish to take a picture of a man glazing at the horizon – in this case, we would like to see in which direction he’s looking at and place him at the right third in order to emphasize it.

The picture on the right illustrates the boat at the end of its course. Notice how in this case the composition is not acceptable, since there is no "interesting story" behind the photo as it is not clear where the boat is sailing.  The central picture illustrates a symmetrical composition.  The left picture creates an acceptable composition: the boat is located at the lower right third of the frame, so you can also see its direction. Notice also how the symmetry in this picture doesn’t "bore the eye", but creates interest.

When can you break the rule of thirds

Do not be afraid to break the rule of thirds in any case it appears that your composition might get improved by it. Whether you’d like the effect of a symmetrical perspective, or whether it’s important to show some more objects in the frame and thus the central object "moves" to the center - that's fine.

In many cases the scene designates the necessity of breaching the rule of thirds.