To piggy back on HD, Audioholics recently had a series of videos on room acoustics with Anthony Grimani, an acoustician, and they get pretty deep in the weeds on the subject. It's above my pay grade, but there's a lot of info in these videos.
There's a lot to it, and you really do need to do some homework and have proper data before putting up any room treatments. From what I've read a common theme seems to be with folks slapping up treatments all over the place, over-do it and completely deaden the room, which you don't want.