Decorate with candles, lava lamp and figurines.
Inexpensive at the Dollar Store or thrift stores. (Goodwill/St. Vincent Depaul)
Impressive wall art or abstract, fractal or blacklight poster above your headboard.
Here are some DIY ideas.
Wall Decals (amazed how expensive they are)
Use contact paper ($5 a roll) cut out any design, tons of colors and easy to remove without damaging walls.
decor yourself < watch video, instructions after commercial
Message Board, pushpin/tac up notes, photos, memorabilia...
Cut a large square out of box cardboard, about the size of a cork board.
To make the hanger, punch two holes 1/2 inch apart 1 inch from the top in the center, thread the ends of a twisty tie (the paper covered wire used to close bread) thru the holes, turn it over, make a loop and twist the ends.
Cut a piece of fabric 2 inches larger than the cardboard.
Lay cardboard on top of fabric and wrap to the back like a present and glue or pin.
(you could use an old shirt or sweater or a shirt with a cool design or your fav band
cut the front of the shirt two inches bigger than the cardboard)
Wall Art Panels
Cut one large or two matching size rectangles about 12"x20" out of box cardboard.
Make the hanger as above, wrap with contact paper, cool wrapping paper, wallpaper or fabric, glue to the back and hang together on one wall.
For thicker panels glue layers of cardboard together.
Cut out any size out of thin cardboard. (a cereal box works great)
Make the hanger.
Use a glue stick or a small drop of glue for each pic, you can arrange the pics side by side or overlapping.
Group framed photos or nature pics on one wall.
Best to arrange on the floor with largest pic in the middle before hanging or in matching frames. You can frame calendar pics or cut out pics from magazines or print pics from the net and frame.
You can make frames, cut out any size frame from cardboard and wrap with gift wrap, wallpaper or fabric strips.
Or a multi-pic frame
https://www.exitinteriors.co.uk/office-13/superframe-contemporary-perspex-mounted-372-375_medium.jpg <about $3 at walmart
Hang a poster of your favorite band, movie or celebrity.
To make your room look larger, neat and brighter arrange your room in separate areas, with lighting for each area and a lot of natural light.
Hanging a mirror will make your room brighter and appear larger.
Center your bed with the headboard against a large wall or between two windows with a nightstand and lamp or hanging paper lantern.
Place your chest of drawers on the opposite wall across from the footboard.
(unless it blocks a window)
Put your desk/computer table under a window or in a far corner.
Your wardrobe on the other side of the room.
If you have room, for extra storage and seating you could put a storage bench at the foot of your bed.