It is assumed that when you look at a photo your eyes go to the middle of the frame to take in the whole shot and view it naturally. This is actually false. Studies have shown that when first looking at picture your eyes first go to one of the four points of intersection on the 1/3 lines shown in the LCD screen when lining a shot up. It is much more natural for someones eyes to go to these lines of intersection so it allows for more natural viewing. Try to line up the subject, more specifically the focus of a shot, on one of these intersection points for the most visually satisfying picture.