The metal bracket thingies holding up the shelves were visible and you could see gaps where the shelves were cut a bit too short.
I attached 4 1x3's to the existing vertical boards holding the shelves. This makes the whole bookcase look sturdier and hides those metal brackets and short shelves.
I also added crown moulding and base moulding and four additional shelves.
As far as bookcase organization goes, I have shelves for history and geography, shelves designated for science topics, two for young children's fiction, one for books the children and I are currently reading as a part of our lessons, and a few for homesteading/homemaking topics. We have a large quantity of historical fiction and non-fiction which fill other shelves. And of course a shelf for the record player and records so my children grow up knowing just how wonderful vinyl is and how you have to dance soft-footed to it so as not to make it skip. :)