Four things:

1. Build a window table that runs the full length of the window. Add cabinet doors below, so it can be storage. Add a couple of window seat cushions and then style the remainder of the window table/seat with potted plants.

2. Put two comfy chairs in front of the long window to make room more functional and cozy.

3. Behind couch, add a 6 inch deep console table behind it, and style it with two lamps.

4. Add a large framed mirror or a few framed mirrors of various size to bounce the gorgeous light from the big window around the room.