Mine are organized by size. Largest book at the right end of the shelf leaning against the lower edge of the bracket above, in order by size down to the smallest "normal" size book at the left end, held in place by a stack of small paperbacks and patterns. Not a very good way to do it I admit since it makes it a little harder to find what I want unless I know exactly what I'm looking for, but the shelf looks cleaner that way.
Cari