Read all the other screenwriting books (Field, Haug, Vogler, Truby, McKee, etc.) - I will say this. All that other stuff is relevant and needs to percolate in your head, but Pilar's book is a real workbook.
Let's put it this way: when she says from concept to page, she's not kidding. You fill out these worksheets and you get to brainstorm, outline, beat out, and break down the story of your screenplay. And only then do you actually get to write the first draft. The fact that chapter 5 is titled "The First Draft" gives you an idea the amount of work you are putting in with chapters 1-4! Other reviews break down the chapter titles, so you know that you will get help in rewriting your first draft.
What a great book. You still have to sit there and figure stuff out, but, instead of just sitting around asking yourself "how do I get from point A to point B?", Pilar will help get you there by asking you the right questions.
Kind of like Socratic learning, right? You can't figure out the correct answer if you don't know the correct question. Pilar's book asks the correct questions. Now, get writing!