Ideally you should treat the front and back walls as a priority. Secondary will be the fireplace and your shelves at the reflective point where you can see a mirror reflection of your speaker while sitting down in your listening chair. We need to use absorption/duffusion on the front wall and diffusion on the back wall. Check out the cool traps from ASC a neat pattern can be created on the front wall in the color of your choice.
http://www.acousticsciences.com/lsa/cooltrap-flyer.pdf