Well just as a basic layout - here's a start - I'd use your back "focal" wall (the one with a canvas hanging on it now) and I'd begin to create a nice vignette that would have your 2 bookshelves flanking either side of a painted desk. I'd also hang a great piece of art (or mirror maybe) over the desk. Find a statement chair for the desk (or a great vintage french chair you could slipcover or upholster or even paint)

I would also make sure your bookshelves are full height in the space so they don't look puny! Then I would float your 2-3 slipcovered shabby chic club chairs in the center on an area rug with a great round ottoman in the center of them. I'd hang another larger piece of art (or large french leaner mirror) on the left wall (where your black bar is hovering near). Find some wonderful gauzy sheer linen or other fabric for your window treatments to keep things in that Shabby Chic breezy vibe! Depending on the colours of choice - find a great neutral for your walls (gray leaning, Benjamin Moore Revere Pewter, warmer leaning Natural Linen or Grant Beige or Pratt and Lambert Feather Gray (great with linen) ) all are very light and airy.

I hope this is a good start to your inspiration for your new decorating project! Have fun with it and enjoy your hunt for some wonderful things :)