To start, I would pull your couches off the walls, so their front legs are on top of the rug. It will make the room feel cozier.

Secondly, I would try to lower the tv by finding another place for it.

Some ideas... to add contrast and interest to the room you could pull one of the darker colours from your area rug and paint the entire fire place wall that colour. I agree the ladder shelf looks a bit insignificant so relocate it and because the fireplace is bumped out, the inset areas on either side are perfectly suited for built in shelves. You could leave the deep background colour on the walls and just have ( custom preferably) floating shelves installed. They should have a beefy looking profile so they don't look wimpy in your grand room and could be in a matching wood to your current wood treatments. You then have a place for large baskets, books or art pieces. Keep the pieces large scale and you could introduce an accent colour in your decorative pieces for contrast. Next tie in some coordinating cushions in the same accent colour for you couch.
I agree pull the couches on to the rug so they don't look like they are floating in the room and for better conversation flow. For the window treatment use one large curtain rod and hang it well above the 3 windows, approximately half way between the ceiling and window frame. Curtains should be full enough to cover all 3 windows to be in keeping with the large scale of the room.
When you select accent pieces such as cushions think about texture as well as colour. You may want to include a faux fur cushion and a chunky throw to provide interest and warm up the room.
Without seeing the other walls it's hard to recommend art work but because of the scale of the room and your furniture, a large piece would likely work best ( hung with the centre of the artwork at eye level) in neutrals with a pop of the colour in it that is present in the accent colour that your choose. ie: red, burnt orange, mustard...you should love the colour! All these things combined will warm up the room, provide visual interest and make it appear more curated and enjoyable to be in.
You have great bones already!

I love the ideas stated and was also goong to suggest pillows and a throw in your favorite bright color

We need to see all the walls. Post a picture of the wall opposite the windows. Looks like the "4th" wall is open to another space? TV is way to high over the FP. Is this a "formal" LR or more of a family room?