I think decluttering will help to calm down the room a lot. With books placed horizontally on top of vertical books, and every nook and cranny full of things, there's just too much to look at.

What about painting the wardrobe to a lighter colour? It's very dominating in the space. If there was room, I would stash away all the books etc. in a bookcase which would have a door over it, but it looks like that isn't an option here.