Research into the Principles of Photography:
Rule of Thirds:
The Decisive Moment:
The basic principle behind the rule of thirds is to imagine you are breaking down the image into thirds, both horizontal and vertical so that there is 9 parts to the image, like the example above. You do this in your head so that you can identify the important parts of the image, which is four parts of the image. The four lines that help with the rule of thirds are also useful for positions of elements in your photo.
Basically, the decisive moment is the moment that the photographer decides to take their shot. This concept comes from Henri Cartier-Bresson who is a photographer and photojournalist. It refers to capturing the event that is ephemeral and spontaneous, where the image represents the essence of the event itself. In other words, the decisive moment captures the subject of the image in action and naturally portrays the event.
When photographers talk about the depth of field, they are referring to how much of the picture they choose to have in focus. For example, if you are taking a close up still life image of some flowers, and you only focus on the closer flower, this would mean that the depth of field of that image would be focused on a particular flower. By choosing the depth of field, you are choosing what part of the image attracts the viewers attention.