Hey Sarah,
Sorry I've come a bit late to this thread. Over the years, I've adapted several novels into screenplays -- unfortunately, none of them ultimately made it to screen, but the process has proven interesting and I have some advice, most of which may run counter to what you may hear from most people.
As I'm sure you know, novels, movies, the stage -- they're all very different media, each with their own unique strengths and weaknesses. No doubt, based on your experience and creative preferences, when you sat down to craft these stories, you may the decision to develop them in one particular medium -- as novels.
That decision shaped countless other decisions. How you were going to introduce your characters, develop the various conflicts, introduce side narratives, develop the structure. All of that is intimately connected to the medium that you chose.
Now, there are unquestionably some stories that, simply by virtue of their underlying narrative structure, lend themselves to moving from one medium to another with relatively few changes.
The work of Raymond Chandler, for instance, stuck largely to external action and dialogue, with characters moving through external narrative landscapes and physical action -- rendering that work ideal for adaptation.
Very few novels work as well.
So when I have been tasked with writing adaptations of novels, this is what I have done. I've read the novels in question a few times -- and then I set them aside and never look at them again. What I then proceed to do is to sit down and say to myself -- suppose that there never was a novel, that I was all the back at the beginning of the process. I only had, as once the writer of the novel did -- the bare concept of the story. Only now, instead of moving ahead and writing a novel -- I'm now going to write a screenplay.
I am now, in effect "unburdened" but the wait of everything that the novelist wrote. It may very well be that I will write a number of scenes that are similar -- or many scenes, or very few scenes. It may be that I will begin the story in the same way, or a very different way -- because the way in which the character were introduced in the novel might have worked really well -- on the page, but that doesn't mean that that's the optimal way to introduce those characters on the screen.
The way in which characters and conflict were developed on the page may have worked very well -- on the page, over the course of several hundred pages -- but the requirements of doing that work with around a hundred pages, through the requirements of dramatic action, may demand completely different scenes and different decisions.
And I always set out to write the very best version of that story -- for the screen -- that I possibly can. I'm not interested -- and I've always said this when producers ask me about doing an adaptation - in writing a "classic comics" version of a novel -- of writing something that's "faithful" to the book. If you want something faithful -- go read the book. That's optimally faithful -- because that is the book.
I'm taking the underlying concept and doing my best to create the very best motion picture I can, based on that concept, on that underlying premise. That may be quite similar, or it may be very different.
I'd also like to point out that in the two cases in which I wrote adaptations of novels that were very different from the underlying books, both authors, when shown the scripts, responded very positively -- because they understood that my job wasn't to attempt to duplicate their work on the screen -- but to create a new work, tailored to be the best movie that I could possibly write.
So that would be my advice -- go back to your initial premise, your initial inspiration and, to the extent that you can, forget about the novel -- and simply start asking yourself -- what is this "movie" going to look like? What's the opening scene? What do the first two pages look like? The first ten pages? The first act? How do I introduce the characters through action in a way that's memorable?
Those things may correspond to elements in your novel or they may be completely different. Don't worry about the novel. It's still there. Your goal is to create the best screenplay for the optimal movie version of this work.
Hope that this is helpful.
All the best
Neal Marshall Stevens