Color co-ordinate your books to create a visual impact.
Instead of piling up one big bookshelf, you can create a themed collection of books. Teamed with appropriately -theme bookends and place each collection in a different room of the house.
Mix up your display by stacking some books vertically and others horizontally. Use the horizontal stack as a platform for an ornament, thus adding height and making it a focal point.
Introduce an ornament or picture frame places off-center to add interest, but leave the odd empty section open to create some breathing space.