Wow! Thanks for what you do. I really could use some advice for my family room. Starting with the basics: paint color, window treatments and furniture layout, etc. The upholstered furniture and carpet are very worn and need to be replaced. I tend to choose classic simple pieces. I gravitate towards greens, browns, purples, red and dark wood. I’d like to have the fireplace stand out. I’m also stuck with what to do on the left wall.
Try chairs of different sizes. I figure out exactly what size would look best on paper- and then go find that size of chair. This helps you to not have chairs that are too small or too large for the room. I also keep in mind if this is a "lounge chair" or a decorative chair. For lounge chairs I like to have at least 36 inches of depth with a tight back, and 38 inches with a pillow back (generally speaking).
Maybe you would like the two sofa look instead...
This goes for deciding your quantity and size of tables as well. You can check yourself with some blue masking tape on the floor to make sure that you have given yourself sufficient walk spaces.
Maybe you have room for two sofas and two chairs. Ask yourself how many people you want to seat in the room- and then see if it will work.
Then you need to start somewhere- perhaps you will find a chair and fall in love with it... maybe it will be a fabric for your drapes... you need an inspiration piece to chart your color pallet and path. I wouldn't try to fit both red and purple in the room. (chair from Horchow)
After you have a fabric to work with- it will be more clear to find others that coordinate. This is a drapery fabric from Beacon Hill. Have your panels- four on the large wall of windows- and the two on the wall with the TV- all hang at the same taller height. Layer your window treatments with woven woods or a solid color Roman shade. I would pull out the dark neutral khaki shade for a carpet color- or better yet- continue with your stone floors and put in an area rug. (is that Jerusalem Gold limestone?) The rug at the top of the post is from Homedecorator.com.
It looks to me like your sofa is pushed up against the pony wall. I would push everything closer to the TV- pulling your furniture into the room. What to do with the left wall??? It looks to me like your door and stereo components are filling what I can see- but you do need some art and wall decor in your room.