The rule of thirds is one of the most basic composition guidelines in photography. The rule of thirds makes use of a natural tendency of the human eye to be more strongly drawn towards certain parts of an image.
What is the Rule of Thirds?
The rule of thirds is an imaginary tic-tac-toe board is drawn across an image to break it into nine equal squares. The four points where these lines intersect are strongest focal points. The lines themselves are the second strongest focal points.
How Do I Use It?
To use the rule of thirds you need to imagine the grid on all of your images as you compose them in the viewfinder. If you have an autofocus camera You can use the autofocus points as references to help you imaging the grid. If you use an LCD screen to compose your images you can make a rule of thirds grid out of a clear sheet of window cling material. Another option is to draw the grid on your viewfinder (not lens) although this may not be easily removed and should be avoided if at all possible. With a little practice you will be able to effectively imagine the grid placement as you shoot.
Does it Matter Which Point I Use?
Which point or line you place your subject on does matter. While any of the points/lines will add emphasis to your subject, some are stronger than others.
When an object is alone in an image, the strongest position is the left hand line. An exception to this is for cultures where information is read right to left, in those cases the right hand line will be strongest.
When a subject is not alone there is a hierarchy of image strength. The subject in the foreground will naturally have more strength than the subject in the background. However, the rule of thirds placement can emphasize or reduce this strength. The bottom right point is the strongest for multiple subjects and the upper left point is the weakest. This theory is often used in movies to convey the emotional dominance of one character over another. Placing a background subject on the right and the foreground subject on the left will confuse the eye and lead to confusion in the viewer about which subject is dominant. This technique is very useful for emotionally-charged images.
Another general rule (although this rule can be broken in certain circumstances) is that your subject should be placed on the opposite line of the direction your subject is looking towards. For example, a portrait where the subject is looking to the left should place the subject body on the right.
How Does the Rule of Thirds Work in Portraits?
While most good portraits appear to be simply a centered torso they are following the rule of thirds. In the case of single portraits, the subject's eyes are placed along the top rule of third line. In multiple subject portraits the subject faces are placed on the rule of thirds lines. This is why a multiple-row posing generally works better than a one-row posing.
Additional Rule of Thirds Examples
Rule of Thirds Zone Method Details