Composition is the reigning artistic element in photography. In a basic sense, it is simply lining up a picture correctly. However, correct composition has been debated throughout the history of art. In artistic composition there is a theory that asserts a perfect composition, and it reigns true in most cases. In its simplest form, it simply states that the focal point of works of art should not be located directly in the center of the composition. This is not pleasing aesthetically, but minutely off center to either side makes for more of a pleasing balanced composition.
This is true for every form of composition including landscaping and portraiture. Many advanced photographers may stray from this rule, but it will take amateur photographers a long way towards becoming very skilled. This is not a rule as much as it is an observation that has been made over centuries of art and art viewing. It works well when viewing a potential photograph through a view finder. Some artists have an innate ability to compose pictures well, but remembering to keep focal points somewhat off center when lining up shots will suffice in the beginning. Eventually, the photographer will simply know a good shot when it presents itself.
However, there is a divide in the natural view that a person visualizes with their eyes and replicating that scene in a photograph even with digital technology. Practicing proper composition will make it more possible. A simple technique for practicing good composition is to take all the successful photographs of a photographer and point out the features that make them visually pleasing. Beyond lighting and other artistic elements, they will all have great composition in common.