Granted, it does depend on what stage of the journey you are at, and on what you are looking for: Are you are looking for ways to begin or motivation? Are you looking for ideas about developing or improving your craft or technique? Are you looking for agents or publishers or are you keen to know what they are looking for?
Below is a list of books that I've found very useful and/or have seen recommended in a number of places.
For the beginner:
This Year You Write Your Novel by Walter Mosley; On Writing by Stephen King (Both offer practical advice and motivation.)
For the already committed:
The Poetics of Aristotle by Stephen Halliwell; Story by Robert McKee; Writing the Breakout Novel by Donald Maass; On Becoming A Novelist by J.C. Gardner; Techniques of the Selling Writer by Dwight V. Swain; Rhetoric of Fiction by Wayne C. Booth; The Art of the Novel by Henry James; Fiction Writer's Handbook by Hallie Burnett; The Writer’s Journey by Christopher Vogler; Stein on Writing by Sol Stein; Plot and Structure by James Bell; The Writer's Essential Tackle Box by Lynn Price; The First Five Pages by Noah Lukeman; Self-Editing for Fiction Writers by Browne and King; Revision and Self –Editing by James Bell
And, for the ready to be published:
Jeff Herman's Guide to Book Publishers, Editors and Literary Agents by Jeff Herman (Refers to
You can get all of these books from somewhere like www.bookdepository.com for around four hundred dollars, which is about the same price many book doctors charge for a manuscript appraisal. (I’ve paid double that for a manuscript appraisal and gotten far more useful information from the books.)
I personally think studying books like these, written by people who have spent decades writing, selling, and/or teaching how to write fiction, and making notes on what you can apply to your manuscript to improve it, is the best way (along with regular fiction reading and writing) to develop your fiction.
Hope some of this is useful.