Try a large basket in the lower left with wood for the fireplace. Try high heat black paint on the brass insert and replace it. I see a mash of books on the left center . . try stacking like colors horizontally in several cubes - the one above, the one to the right in the center and use your photos and "knicknacks" with the books in each cube. Take the little things off the mantel, get a piece of art you like, that echos the colors you want to use in the room (bluegreen in upper right?), frame it in white simple frame to echo the mantel and add only two more elements back to the shelf with it . . something tall and pretty, something small and 3d. ..

First, paint the brass firescreen with heat proof matte black paint for a quick update. If you like big accessories like the platter on the right, then make a coordinated display in the shelves of similar or like items, such as a collection, using one stunning piece per shelf. If you prefer more conventional decor and shelves, add shelves to fill in the large open spaces and style with 1/3 books, 1/3 decor items and 1/3 open space. Smaller items can be grouped in threes, fives and sevens, if you like.Your room doesn't show us much in the way of furnishings and accent colors you are using unless the wall on the right is your accent wall. If it is, then that color should drive the design theme for color - you need items that work with it or match it.

Painting the fireplace and accents of the shelving black could work out beautifully. it seems like your wall unit and other furniture is dark in tone and adding some black to the wall could work that in and provide some contrast.

Here are some other shots of the room - it's kind of an odd space. As for colors, I like the colors in the pillow fabric.