If we spend as much time jerking with the room as we did looking at new audio gear, we would have already developed a sense of intuition about room acoustics.
I think most of us who don't have a dedicated listening room may never know how good our systems can sound with everything in its right place. But I also know, having been in a few listening rooms, that sound really doesn't care if you have a dedicated listening room. You can tilt your living room in the right direction with very smart choices in decor.
Rugs, absorbtion and diffusion panels are great but the ceilings are also important. The best rooms I've been in had great ceilings.
Got a room with a flat ceiling? Got all the usual stuff done? Focus on the ceiling.
Haven't started thinking about acoustics? Focus your first efforts on the front wall and the side walls, ceiling and floor that extend 20-30% toward you. This is the most critical area. Softening this area will sharpen the focus. Everything else is also important but start here.
That's just my intuition.