for profit rather than bananas. I have the library divided in parts.
Reference.
Humor. Including books of cartoons.
Art. There is some overlap with humor.
Fiction. Mostly interesting but not worth much money.
Non fiction. Tough to sort if the collection isn't worth cataloging. The sort is the catalog. Alpha order by something is an obvious choice. The question is alpha order by what?
Author if the author has important books on more than one topic.
(edit) Author if the author has only one book in my library not obviously cataloged elsewhere.
Subject if I have more than one book on a subject.
Biographies are about a subject.
So are some modern nations, e.g. China.
Books without an ISBN are special. For one thing they might be old and they are trickier to sell on Amazon.