Generally speaking, splitting the frame right down the middle is not necessarily your best option. While it may seem more balanced, it can actually be pretty boring. You should utilize the rule of thirds when deciding how to divide your frame.
With horizons, a low horizon will give a sense of stability to the image. Typically, this is done when the sky is more appealing than the landscape below (Figure 9.11). When the emphasis is to be placed on the landscape, the horizon line should be moved upward in the frame, leaving the bottom two-thirds to the subject below.
Also, don’t think everything needs to be split along horizontal lines. Even though the horizon line in Figure 9.12 is roughly centered, the frame is split into thirds vertically by positioning the bridge and its reflection at the right edge.
Frames within Frames
The outer edge of your photograph acts as a frame to hold all of the visual elements of the photograph. One way to add emphasis to your subject is through the use of internal frames. Depending on how the frame is used, it can create the illusion of a third dimension to your image, giving it a feeling of depth.