Hang up anything that is you. Put contact paper on old hat boxes, large wall panels, storage boxes, etc. Bed spreads can be coordinated with draperies. Put on decorative trim around bulletin boards and picture frames. Colored masking tape around collages or ends of fibre board will make a frame around posters and add stability.
Match pillows with the fabric of curtains or spreads.
Put down something like an area rug. A painted orange crate makes a good storage space for books. Add pillows, an inflatable chair or a bean bag chair. Arrange boards and bricks for a book case or a stereo stand. Also include live plants, dried flowers and anything else you feel will add to the overall effect of your room.