Preserving the Wood Is Imperative
The room must be conducive to preserving good wood while it also helps animate the sound. And perhaps the single biggest concern for all that is the room's climate, its atmospheric condition. Important questions concerning the piano's welfare are questions about moisture content, air currents, drafts, fluctuations in heat and/or cold. Atmospheric concerns are so important, in fact, that the climate even outside the room is also important. What is to be done inside the piano room is directly tied to what kind of climate the house resides in. Is it desert outside? Is it the humid North east or west? Is it the muggy South? Efforts to control humidity inside depends on this.
Often, especially with musicians specializing in electrically amplified music, soundproofing comes to mind when asked to imagine a perfect music room. Soundproofing might be important if the piano is in an apartment house with thin walls, but usually soundproofing isn't necessary when the music room is for a piano or other non-electrically amplified instrument. Soundproofing, too, can be a detriment to the acoustics of a room. In trying to shut out sound, soundproofing often will deaden the sound remaining.
More: Your Piano Wants Company: Furniture that Goes Well.
Also: Tips for Taking Care of Your Piano