Select one large piece of furniture, such as an antique iron or brass bed, a large armoire or a dramatic velvet sofa as the focal piece for your room. Ensure this piece is large enough to make a strong visual impact but small enough to fit comfortably between the angled walls.
Install curtains along the top of the angled walls to provide soft, draped edges to your room. Long, soft drapes that run the length from the ceiling to the floor will lengthen the wall, making the room look taller and providing a romantic feel to your room. If ceiling-to-floor draperies aren't your style, consider installing vintage linens on the windows of your slanted wall room to diffuse light and give your room a comfortable, lived-in look.
Just because your room is small doesn't mean that it cannot have a dramatic visual impact. Don't be afraid to saturate the walls in a bright, vivid color. A bright color on the walls paired with a light color on the ceiling will make the room look larger. For an eclectic look, consider installing wallpaper on the walls in a fun print or, for a more subdued look, use more subtle, classic wallpaper such as a stripe or muted print.
If the walls of your room are slanted at such an angle that the side walls are rendered nearly useless, consider building a bed into the wall to make use of that formerly unusable space. Build a bed frame with 4-by-4s and consider installing a sliding curtain to provide privacy for the user of the bed. Make the frame big enough for your mattress and install lots of comfortable, fluffy bedding and pillows so that the area becomes a comfortable respite. Consider installing a wall-mounted reading light as well.
On a sloped wall, make use of seemingly unusable space by building shelves into the wall and filling the shelves with books, display items, baskets for storage, toys and other things you want kept out of the way.