Spring Cleaning: Bookcase Edition

I'm in the process of reorganizing my family bookcase...although commandeering is probably the better term to use. While my mother has insisted that I cannot remove the 1995 encyclopedia set that we have on the bottom shelf, I have managed to free the top four shelves for my own use. After staring at the boxes and boxes of books that I have, I'm not sure how best to organize the books. Should I alphabetize by author? Should I organize based on reading level? Should I arrange according to genre?

In a way, I feel like Liesel from The Book Thief as she runs up and down the rows of books in the mayor's wife's library. So many choices...so many options!

As a future teacher I know it might be valuable to organize my books based on reading level, but I haven't read all of the books I own yet, so determining the reading level of each text might take a great deal of time and research. In comparison, arranging the books according to genre might help me make reading recommendations to my students next year. However, many books span multiple genres, like Suzanne Collins's The Hunger Games. (Is it fantasy or is it science fiction?!?) If I organize by author then I can always find a book that I'm looking for without worrying about its location.

One of the reasons I'm devoting so much time to this spring cleaning project is that I'm not sure what my job situation will be like next year. As a new teacher, there is no guarantee I will have my own classroom. If I had my own classroom (with a nice set of bookshelves), I could easily transfer the books from my private collection to the classroom. However, if I do not have a space to call my own, I might need to keep my book collection at home and bring in a handful of recommendations at times.

Any suggestions as to how I can best reorganize my books?