All you want is the yolk, so the shell and the other stuff goes down the disposer. But the yolk doesn't do much good just sitting there by itself. That may sound obvious. But when you're just starting out in this business, odds are the novel's structure will end up gripping your play like a vise. Some of the villains here . . .
Novels are able to tell vast stories.
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.