How to organize class library?

I will be starting my first teaching job in August (kindergarten). I am slowly collecting books for the class library. How do you guys organize the books? I have seen by author and genre/interest, but I have also seen them organized by reading level (F & P). I was thinking of combining the two ideas, grouped by genre and another marking for reading level. This would help students find books that interest them in their level, as well as help me keep inventory of what genres and levels I have, and if I need more of a specific type of book.