I did some research into what makes a good, effective and eye catching book cover.
Focal points – These are the points at with the eye is naturally drawn to subconsciously.
Size – Objects at or near to the center of a design tend to grab attention more than similar sized objects in other areas of the page do.
Isolation – Surrounding an object with white space draws attention to that object.
Contrast – Bright and dark objects placed near to one another create strong contrast, which gives a more eye catching design and the colours make the objects leap off the page.
Convergence – Lines within the design can point to, or converge on a word or object to increase its point of focus. The eye will naturally run along a strong line, or multiple fine lines. four small lines bring a surprising about of emphasis to the focal points.
Book covers love the rule of thirds. The premise of this rule is that when key elements such as graphics or type cross the page horizontally at the devision of thirds, as opposed to in half, the image is more appealing.
Preferred Diagonal Scan – Because westeners read from left to right, and top to bottom, our eyes tend to cross the page in a series of sweeps. Our eyes are naturally conditioned to feel comfortable with designs that have an upper-left to lower-right flow.