Can you work out what's annoying you the most about the room?
I moved house about 3 1/2 years ago and still working on it, but basically there's usually something that really irritates me, so I tackle that first, then move on to the next thing. It means none of the rooms are really "done" but they are all liveable.
Having now had two home offices in different places, the things that annoyed me most were: clutter, lighting, and feeling cramped.
So, I spent at least a day tidying up - bin / recycle - got more shelving space, a new desk that I though was bigger than I needed (pro tip - they never are!), some storage boxes for bits and pieces, and new lamps. All that was from Ikea so didn't cost a fortune.
Lighting for me is really important as I do get migraines from time to time - I need at least one desk lamp, and as little overhead lighting as possible. I prefer to have at least two sources of light at "desk" level, and a standard lamp if I need more light. Also sit the desk so that i'm shoulder-on to natural light.
Sorting each place was hard work, but by the end of it I had a much happier working environment even though it was the same floor space.
If your issues are more cosmetic than organisational, I also have a couple of motivational quotes and usually a couple of landscape photos / prints hanging up to one side - not in front of me, as I'd spend all day staring at them and not working. Oh, and lamps, too! Softer / better lighting makes a massive difference, in my experience.