Writing a novel can be an enormous challenge so here are two books that may help you along that path.
Writing and Selling your Mystery Novel
by Hallie Ephron
The first is a book by Hallie Ephron called Writing and Selling your Mystery Novel. Don't let the mystery part of the title put you off either because I'm sure that whatever genre you're writing, you'll find this particular book helpful.
Well worth reading for the aspiring as well as the seasoned writer who has become blocked.
My second recommendation is Mid-Novel Writing Prompts and as far as books on prompts go, I must say, this is the best I've come across.
Mid-Novel Writing Prompts
by Rayne Hall
If you've run out of inspiration (as we all do at times) you may just find these prompts help stimulate your imagination and set you going again.
100 prompts each with ideas on how to use them, what-if scenarios, and suggestions for how you might interpret the topic.