The best place to start is the rear wall behind your listening position (diffusion and bass absorption).
Sharp cabinet edges should be avoided within about 3 feet from the front baffle of your speakers (edge diffraction). I would keep the side walls clear if you can so as not to "crowd" the speakers...leave 3 or 4 feet between speaker and side wall so you can sit further back in your room and still get good imaging. Acoustic panels/fabric wall hangings on side walls at "mirror" points can always be added to your room if it sounds too "live" for your tastes....however bookshelves are a more permanent addition that you can't adjust easily to gauge their impact.
Sharp cabinet edges should be avoided within about 3 feet from the front baffle of your speakers (edge diffraction). I would keep the side walls clear if you can so as not to "crowd" the speakers...leave 3 or 4 feet between speaker and side wall so you can sit further back in your room and still get good imaging. Acoustic panels/fabric wall hangings on side walls at "mirror" points can always be added to your room if it sounds too "live" for your tastes....however bookshelves are a more permanent addition that you can't adjust easily to gauge their impact.