I am in a similar situation. I have 12 by 12 room and the squareness(is this a word?) is the killer here. I've had some success in making it work.
1) If this is a dedicated listening room and you can do it, position the speakers at 90 degrees (in other words make a diamond shape rather than a square) this is the best thing you can do to improve sound in your square room.
2) if you have bass issues, bass traps DIY or pay a pile of money for commercial ones. My bass it solid, not over powering so I removed my DIY traps which worked too good.
3) Flutter echo
4) 1st reflection points, don't forget the 1st reflection points on the ceiling and back wall.
Flutter echo made my room very bright, also I put acoustic foam in the corners.
Hope that helps. My room is tolerable.
Rob