A small room feels bigger when the eye can travel through it. That usually means less on the floor and more light on the walls.
Start by taking out one piece of furniture you rarely use. Raise what you can: shelves instead of side tables, a wall lamp instead of a floor lamp.
Hang a mirror opposite or beside the window so it carries the daylight further into the room. Keep curtains light and pull them fully open during the day.
Finally, clear the surfaces. A few chosen things on a shelf look calmer than many small things everywhere.