If you have semi-cluttered shelf space here and there you can't quite get to look cohesive, some random items that need a home, or floor-to-ceiling shelves in your new digs, here are some basic tips.
The Right Group
A kitschy animal statue with a plant and a stack of books? Perfect. Four animal statues on one shelf? Makes for a cute manger scene, but runs the risk of a Grandma Collecting Cat Figurines vibe. Plus, an unexpected juxtaposition of items can showcase them better than lumping like items together. Group with odd numbers, and vary the heights/widths of items for visual interest. Curating? Scout large knotty driftwood on your next beach trip or browse a neighborhood estate sale for weird, unexpected, or meaningful items.
Repeat Bold Colors
Unless the object in question is an accent wall or a dramatic focal piece with no other colors in the space, repeating color throughout the room ties things together. I am currently loving jewel tones like emerald, marigold and burnt orange, so a few of these items on the shelves can bring a fresh look to your whites and neutrals.
Be A Bookworm
You can definitely style shelves with just books. For awhile color coding them was hot but it was a little OCD for my taste. If mixing books with objects, vary them vertically and horizontally to keep things balanced, using roughly the same thickness/height for each stack or grouping. If your collection amounts to heavy outmoded school texts or a childhood selection of Goosebumps novels, just turn the spines to the wall, or cover them with white, metallic or colored paper (or bind several together if they are thin). I won't tell.
For large shelves of book collections, thrift a unique ladder that screams "old library" and invest in some large, live plants in floor pots.
The Shelves Themselves
Installing LED lighting, wallpaper, vintage frames, or accent colors behind built-in shelves or bookcases can look nice, especially if you have a lot of empty space, but be sure that the backdrops of your shelves aren't competing with the objects on them.