Avoid mixing color images with black and white images. Paint the back wall an accent color to make accessories pop out. Or conversely, paint the unit the same color as the room's walls so that the emphasis is on the pieces, not the shelves. But for large collections, display only a few pieces and store the rest, rotating them occasionally. Lean pictures on mantels and bookshelves to create a variety of heights.
Book stack gives height to a small container.
Books, CDs along the front edge of shelves for easy access. Too many small items and no focal point. Trays, baskets for holding remotes, coasters, magazine stack. Space beneath table utilized as well. Painting too small for fireplace.