It has a king sized bed.
Keeping it clutter free is one way. A large mirror also gives the appearance of space. Also light colours on the walls make a room look big.
You may start with your walls by painting it white or off white. Stay away from dark colors on bed linens. Refrain from putting a lot of Knick knacks. And perhaps changing your bet to full size bed will do the trick if you’re the only one using the room.
Here's a bunch of suggestions for you::
You can use light color paint and hang curtains floor to ceiling.
Clutter is the enemy of a small room. Pare things down to just the essentials. Keep surfaces clean and sparse. Use a few large paintings or a large mirror instead of lots of small prints. Mount ceiling or wall lamps instead of using table lamps. Choose a simple color palette and use it throughout. Keep your furniture light. Dark furniture takes up a lot of visual space. If possible, use blinds for privacy and sheers the same or similar color to your walls to create an airy look. Keep the sheers or curtains open rather than closed.
Large mirrors are useful to making a space feel larger.
Minimal furniture, bright wall covers, lots of lighting, and mirrors will make a room feel larger.
If you have side tables considering making/getting floating shelves to free up floor space.
White ceiling and light colored walls. Light colored bedding with colors for pillows. Add a large mirror opposite a window to reflect light into the room. Small bedside tables or wall mounted shelf for clock and lamp.
All of the above suggestions are great. The less furniture the better and consider using under the bed for storage of less used items or seasonal clothing. That way you can either put your dresser in your closet or keep the things that would be in a dresser in your closet to free up space.
Declutter the room smaller furniture
You could get a smaller bed. Mirrors can help expand the look of a room. Light color paint always expands the look as compared to dark walls.
Keep everything monochromatic, it'll make the room appear larger. Have as little furniture as possible, nothing oversized, and no clutter.
I would paint the walls a lighter color and try to have minimal furniture in the room if you can. Maybe add storage space to under the bed or in the closet, if possible.
Agnes: a neutral color palette will help make a bedroom look larger. Also, I got a comforter with lines that made the room look larger. (I continued those lines in a canvas above my bed). Here's a photo:
Scale your furniture a bit smaller it works wonders.
I would paint it a light and bright color