The rule of thirds in photographic composition is one of the very basic rules and taught to budding photographers and entry level aspirants in the stream.
The rule of thirds is a fundamental rule in photographic composition. Basically you align the areas of interest in a composition such that the resulting image draws more interest and reaction. An image can be divided into 3 parts horizontally and 3 parts vertically resulting in a 9 part grid. An intersection point of any of these two lines is called a power point.
The rule of thirds basically states that aligning the areas of interest in the composition with the power points results in an image that draws higher level of interest, energy in the image and viewer reaction. The resulting image is thus aesthetically pleasing and looks professional. Additionally, the areas of interest need not be at one of the power points but in fact they could be aligned to one of the vertical or horizontal lines. This works best when shooting images having horizons or other surfaces.
Most of the newbie photographers or end-users like to place the subject in the center of the frame. This results in a boring flat image. The rule of thirds is practiced in interior design, web design and painting amongst other fields. The right placement of the subject draws more viewer interest and results in a professional composition. Most of the professional cameras have good viewfinder grids which will allow you to experiment and get a better hand at testing the rule of thirds.