In web design vertical lines tend to represent or create length and indicate to the user that there is more content below the fold. Horizontal lines generally create relaxation or a calming mood, they tend to be quiet and subtle whereas vertical lines are more imposing and powerful.Objects in a diagonal position are unstable. Because they are neither vertical nor horizontal, they are either about to fall or are already in motion. The angles of the ship and the rocks on the shore convey a feeling of movement or speed in this stormy harbor scene.
Having it be too much or to little, finding the right amount of props, and be careful if they don't go with the theme or surroundings, you want it to look put together and have that pop