Where to start with room treatments?

Hello all,

Unfortunatly,I do not have a dedicated room, but I do have a nice 2 channel system. However, between my speakers sits a entertaiment cabinet with a 36" TV screen . The room is a living room that strechs into a dining room, ceiling hieght is about 9'. Beyond the left speaker is a sliding glass door to the deck and to the right is the extension of the room into the dining room. i.e the set up is along the "long" wall of the room.

Where do I start when thinking of adding room acoustic treatments. There is no room for bass traps...Ceiling corners? Hang someting on the wall behing the couch (listening seat)?