My bookcase was positioned on the wall leading to the hallway, but in full view of the living room where the Gryffindor Common Room was located. I figured the perfect way to incorporate it was to turn it into the restricted section of the library. I bought huge chains from the hardware store. Luckily someone was there to cut them to the length I needed.
Then I bought a plain wood plaque, stained it, and with an unsteady hand I painted "restricted section" on it. The shelf was then adorned with scrolls, oil lamps, and thrift store portrait.
My guest book ended up being a scroll for everyone to sign and join Dumbledore's Army. I had purchased a real quill and ink too!
The other little details in the Gryffindor Common Room included scarves over my end tables, many oil lams found at thrift stores and flea markets, books, quills, parchment scrolls, etc.