Often when we are taking pictures or creating posters, we have a tendency to put the subjects right in the middle of the page. However, this can make a composition quite stagnant. One trick that motivates a viewer’s eye around the whole of an image is called the rule of thirds.
The rule of thirds is a technique for creating a dynamic composition by placing ‘subjects’ at certain hot spots within a frame.
To achieve the effect, you take your image plane and create a 3x3 grid, dividing the horizontal, and vertical orientations into thirds. Then, if you put subjects or horizons (i.e. where the sky meets the grass) of the image on one of these lines, especially at the intersection of a grid, it imbalances the composition in such a way to enhance the overall aesthetic appeal of the image.
Similarly, the rule of fourths creates a similarly systematic rule for creating an interesting composition by breaking down the canvas into fourths, rather than thirds, and these grids can work with one another to give you a general guideline for where to point your camera or make your first brush stroke.
This is not to say that nothing should ever be in the smack dab of the composition. However, if you do decide to put something in the middle, consider putting another strong compositional element (such as the floor or a large tree) on one of these proposed gridded hot-spots.