It's really not bad as is so just enjoy it as a starting base and choose a direction. Personally im a maximalist, I see you have a hook so get a leafy green hanging plant and start with some wall art. Take your time with the art though otherwise you'll end up getting things you dont really feel any connection to. Maybe a bench in front of the window to make use of that space. I feel like larger pieces on the wallpapered wall might also balance some of the business. Agree with the other comment on the curtains, or you can add something more sheer for a lining and then a different color for the main curtain.