The Rule of Thirds is perhaps the most well known principle of photographic composition. It is not a new rule, this principle applies since the beginning of photography or film industry. Today, with the digital cameras is even simpler to use it. Maybe is something very simple but even so, is also very important rule that give to the final image (or movie) a more pleasant feeling and an artistic look. But, let us not forget that rules are made to be broken or not necessarily used, so feel free to use your own rules as long as the result is pleasing.
What is the Rule of Thirds ? The principle is simple: you must imagine that you will split an image intro three rows and three columns. On the new most digital cameras, in menu, is an option which splits the image as previously mentioned. As you can see in the picture below, the slice of watermelon is placed at the intersection of the two lines in the bottom right.
So, theoretically, when you place the subject at the intersection of any of the four points, the picture gets a special feeling, more artistic and more balanced. Various tests were done which concluded that the human eye usually go to one of the intersection points most naturally rather than the center of the image.
More examples
In the picture below you can see another clear example where I have used this rule. This rule can be applied also in other styles of photography such as landscape photography, portrait and so on. As you practice you will automatically use this technique and you’ll improve your photographic skills.
The most important is to try as many variants and, in time, you will know more quickly where and how to fit main subject. Good luck with that :)