When I first started, I noticed that from the living room I could hear everything my guest was saying in the rental room, even with the door closed.
The floors are tile, and I don’t have rugs because I can’t vacuum (my back). So I bought several inexpensive large area rugs in an unobtrusive solid dull gold color and nailed them up on the walls to dampen sound. It gives the room a much cozier feeling, and is very effective at limiting sound.