List a Condition you know of that will produce Better Sound

For Example:

-Open Baffle always sounds better than a box speaker
-15" diameter Speaker sounds more real than a 6" version
- Heavier Speaker beats a lighter version
- Dual Concentric design beats a separate Mid and tweeter
- Fewer parts in an XO beats more

Okay let the fun begin...

filling the room with artificial ficus trees.  They act as diffusers and absorb sound.  Properly placed, they can really help a room. and improve sound quality.
Play the first song on any cd....take it out and spray the play side with Amour All.....wipe it off and replay first song. WOW. It fills in the pitts on the disc surface and the laser gets a much cleaner, more accurate reading of the musical material on the disc. Try it, you will be amazed at the spacial opening of the soundstage, the cleaner mids and hi's and overall a 25% better sound. Learned this from an audio tech  back in the 80's. It works. Don't put it down until you try it!
I thought the Armor All tweak resulted in a lot of CDs going bad (CD rot). Sam Tellig tried it, then withdrew the endorsement because of those reports.  Anyone else remember that?
Our garage is opposite the rear wall of the listening room.  I store the 4 'spare' summer/winter wheels for our sports car flat against the wall in the garage about midway up.  The added mass improved the sound considerably.