The rule of thirds.
The rule of thirds is basically where you are breaking an image down into thirds. You break it down both horizontally and vertically so that your image will have 9 parts to it like the image below.
With this grid in mind the ‘rule of thirds’ now identifies four important parts of the image that you should consider placing points of interest in as you frame your image.Not only this but it also gives you four ‘lines’ that are also useful positions for elements in your photo.
The theory of the 'rule of thirds' is that if you place points of interest into the intersections or along the lines, your photo will then become more balanced and will enable a viewer of the image to interact with it more naturally. It is known that when viewing images people’s eyes will usually go to one of the intersection points naturally rather than the center of the shot this is due to using the rule of thirds, it just works with this natural way of viewing an image rather than working against it.