Some things I like to keep in mind when styling bookshelves:
1. I like to group books into similar colors. This makes everything look more cohesive.
2. Don't group larger items at the bottom of the shelving unit. This makes it too bottom heavy. I like to spread out the larger items so it looks more balanced.
3. I find that frames can sometimes look lost on a cubby shelf like mine so I removed all of them and put them somewhere else.
4. I also like to group similar objects together. Whether its by color or shape it gives much more impact when grouped together.
5. Alternate books for a more interesting look. Stack some vertically and some horizontally.