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In reference to "Is there such a thing as 'the best (feature film)
screenwriting workbook'?", I recommend Lew Hunter's SCREENWRITING 434.  I use
it in my classes at NYC's The New School.  I don't know if it is the "best",
but it is extremely practical -- he walks you through the complete process
step-by-step while covering the bases of screenplay basics.  And he also
writes his own screenplay as he takes you through the processes.  What I
haven't decided yet is if the script he writes, which is *terrible*, is
either a stroke of pure genuis -- inspiring you, the neophyte writer to feel
confident because you will think, "I can do better than that piece of crap!"
-- or is simply pure and awful writing.
 
In either case, several of my students have used it to help them finish a
first draft and I consider that a sure sign of success.
 
Good Luck!