And they usually do. So Step 1 is to figure out what part of that story can actually be told within the typical Length of a full-length play. Novelists generally use a very early Point of Attack . Except for thrillers. And with those, it's guaranteed that film companies will have snapped up all the rights for adaptation long before you'll ever see these things in your local bookstore.
Most novels use highly Visual forms of storytelling.
That's one of the reasons Hollywood is so hungry for them. It'll just be a minor vampire hovering over your fingers.