Composition

Composition is the art of arrange the visual components of a photo inside the picture.
When you observe the subject of your photo, your mind builds a rich multisensory representation with sound, smell and a wide angle 3D view, so it's not surprisingly that a simple picture can miss some points of interest.
Your task as photographer is just to recreate in a small image all the relevant information working on three different dimensions, the selection of the elements to include in the picture, their relations and the overall balance.

- selection
The rule of thumb is to understand what you have to include and what you have to exclude from the picture.
If you exclude everything that can distract the observer you emphasize the meaning of your photo.
On the other hand you have to look for secondary elements useful to clarify your target, for example in a portrait you can include the something (a tool, a home, a toy, …) to add information about your subject.
You can also evaluate the possibility to shoot at a particular area of the subject to focus on the most important aspect, for example in a portrait you can include only the eyes or the smile instead of the whole body or face.

- relation
After the proper selection of the elements of your picture, you need to have all of them working to strength what your mean.
For example if you are shooting two little brothers, you can focus on how they understand each other or try to catch their resemblance.

- balance
Finally, you have to build your picture, positioning all the elements in a proper way.
Avoid an obvious composition, like putting the subject on the center of the photo – instead use the “rule of thirds”.
This guideline states that an image can be divided into nine equal parts by two equally-spaced horizontal lines and two equally-spaced vertical lines. The four points formed by the intersections of these lines can be used to align features in photograph.
This simple tip will help to obtain more interesting compositions, expecially if you draw the viewer's eyes through the photo using some kind of path, like a street, a row of telephone poles, or a line of chairs.