I'm often asked to recommend screenwriting books. While different screenwriting teachers have different points of view, I think it's worth paying most attention to the elements on which they all agree (i.e., conflict, character development, strong premise). The most recent one I've read far and away belongs in a prime space on your bookshelf.
I refer to The Art of Dramatic Writing by Lajos Egri. Originally published in the 1940s, it was first recommended to me by Tim Albaugh of Hollins University and UCLA. Upon reading it, I've discovered how much a debt screenwriting classics such as Blake Snyder's Save the Cat, Richard Walter's Essentials of Screenwriting, and Hal Ackerman's Writing Screenplays that Sell owe to Egri's work.
Save the Cat discusses the need for a strong logline to precede the writing process. Snyder alludes to the logline as the story's central pillar, the touchstone to which a writer must adhere through thick and thin.
Egri boils this down to an even more elementary principle: the premise. A premise consists of multiple elements, expressed as simply as possible:
1. A point of view. Pick a side. What are you trying to say? What's your voice?
2. A defining character element. Blind belief? Unchecked ambition? Excessive pride? Overprotection? Status obsession?
3. A logical end result of said character element. Tragedy? Death? Loss? The conquering of death?
4. Irony. How does the premise deliver an unexpected turn?
Romeo & Juliet = Love conquers death.
Finding Nemo = Overprotection leads to loss.
Macbeth = Ruthless ambition leads to destruction.
The Social Network = Obsession with status leads to isolation.
Casablanca = Compassion conquers hopelessness.
Birdman = Self-delusion leads to loss.
How do I imagine a premise? I take a page out of Hal Ackerman's book and imagine my character's low point. In his treatise, Ackerman mentions that the most important element you need to know in a screenplay is what happens on page 90. Page 90 is traditionally the act break from II to III. It's the protagonist's emotional low point. It's what the protagonist least desires. The character is as far as possible from what they need. It's also the logical result of their defining characteristic.
Therefore, if you're stuck with regards to formulating a premise, start here:
[Flaw] leads to [low point].
The premise is the DNA of your protagonist. And as character = story, it's the DNA of your plot as well. Every scene and character act must be rooted in the premise. It defines your character, it defines your story. Every piece of your story is a microcosm of the premise. And if you populate your story with complex characters who prove the premise, then most of the heavy lifting you must perform as a writer is done.
Egri also discusses his differences with Aristotle, namely regarding the relationship between character and story (Egri takes the position that character creates story - one with which I agree). And that a truly three-dimensional character must be plotted via the three dimensions of physiology, sociology, and psychology. How a character looks, the circumstances of their environment, and who they are within will each play paramount roles in the actions the character performs to attain his/her desire.
The idea of a unity of opposites also appears in Egri's work. How do circumstances force a character to act? How is compromise impossible, both within and without? Every script, indeed, every scene, must have a winner and a loser. Egri writes, "If we are given the opportunity of seeing how a murderer is forced by necessity, environment, and inner and outer contradictions to commit a crime, we are witnessing the unity of opposites in action."
This is the bedrock upon which shows like Breaking Bad and Better Call Saul are built. How have circumstances forced Walter White into becoming a meth kingpin? What circumstances forced naive young Jimmy McGill to become jaded, cynical Saul Goodman? This is unity of opposites. This is Egri.
As mentioned, the more you read, the better a writer you'll be. If you read Egri, case in point.