What do you like, the room is fairly minimal at the moment, do you like that or would you want something more maximalist?
I've seen people wallpaper wardrobe doors to great effect, makes it a feature rather than a blank wall.
Or you could replace the wardrobe doors with something more lux like a beautiful wood (or more realistically a beautiful wood veneer).
Is that a desk in the corner? Maybe think about hiding the computer and screen when you aren't using it, or if possible moving it out altogether. You could hide the desk away in a converted stand alone wardrobe (maybe an antique or vintage if to your taste). Or do you want a duel purpose desk/dressing table? A mirror on the wall might be nice and a nice desk light? Depends how often you use the desk, don't compromise practicality for appearance if you use it every day.
You desperately need new window coverings. Depending on your taste and budget either some generous curtains or some roman blinds in a gorgeous fabric. Do you need privacy? Some voile roller blinds behind a more luxurious window dressing would give a smarter look than your current curtains.
You've got some nice coving so I'd look for a period appropriate ceiling rose for the central light then get some pretty lighting cord in a good colour (easy to find on e.g. ebay). You could get a long piece of cord and hook the central light in a more practical position, either as a bedside light or above the desk (we did this in the DDs room) or above the chair in the window if you sit there in the evening (could be a lovely spot to read or stare ar the garden). Or you could get a ceiling rose with multiple outlet points and have all of the above and a kind of spider light effect.
A rug under the bed and some bedside tables might be practical as well. Think about what you do in the room and plan what you need around that. And don't think you have to do it all at once, you can add bits piece by piece, especially since you currently have a functional room.