Are there bookshelves with actual books? Or are the shelves only places to put toys or trophies? What types of posters or pictures are on the walls? Are they the parents' choices (usual for children's rooms) or the teen's?
Being sent to one's room used to be a punishment, but not if the child's room also contains a tv and dvd player or computer or game system.
My youngest sister and I shared a dormer room. She was the super-neat child, with everything in its place. My bookcase was always spilling over with books, while her bookcase had some books, but more stuffed animals and dolls. The top of my dresser was where the statues of horses and my rock collection were displayed. Hers had her brush and comb, barrettes and rubber bands for her hair. The shared closet floor was tidy on her side, cluttered on mine. The room was so small we had to do our homework downstairs at the kitchen table. Our play area was down in the basement. Until our two older sisters moved out of the house and I was able to move downstairs into what had been my oldest sister's room, I felt that I wasn't able to put any personal touches into my 'space'. And yet I see that we each did.
If the story is set in a boarding school, there's probably very few options for expressions of personal taste. Dorm rooms in college used to be the same, usually containing two beds, two desks and, if you were lucky, two closets and/or chests of drawers (sometimes the chest of drawers was inside the closet). Then students were able to bring mini-fridges, microwaves and tvs. Now, with laptops and smart phones, the tv is no longer taking up space in a college dorm room, but other items are.
There would probably be even less space on a spaceship. Perhaps the bed might fold into the wall when not in use. Ditto a desk or clothespress.