Here's Melissa Rosenberg on adapting Stephenie Meyers' Twilight books.
There are also regular blog posts, such as this one by screenwriter Don Roos.
If you're trying to write a screenplay, use a Kitchen Timer!
The principle of Kitchen Timer is that every writer deserves a definite and do-able way of being and feeling successful every day. To do this, we learn to judge ourselves on behavior rather than content. (We leave content to our unconscious; experience will teach us to trust that.) We set up a goal for ourselves as writers which is easy, measurable, free of anxiety, and fail-proof, because everyone can sit, and an hour will always pass.