I send all my used book purchases to my parents' apartment in New York because the shipping is twice as much to Montreal. So whenever we go visit them, which is about once a month (visitation!), I have a stack of packages waiting for me in my old closet. It's like a mini-Christmas! So now I have a stack of intriguing books on the shelves in the bathroom.
The one I'm reading now is the cleverly titled
Complications, by surgeon Atul Gawande, about how a surgeon learns his craft. Gawande has a scary and interesting point that the only way for surgeons to become proficient is (as the little old lady responded when the tourist asked her "How do you get to Carnegie Hall?"): Practice, practice, practice. Which means if you are among the early patients he's practicing on, Good luck, Charlie.
Gawande makes the interesting point that studies have shown that the difference between top performers in music and sports and the second-to-top performers is not so much the luck of being born with superb talent as the willingness -- or capacity -- to train. Martina Navratilova crushed her competition in tennis in her day because she was the first woman player to train as if it was a full time job. The other players were practicing by playing tennis. She lifted weights and ran and hired a nutritionist. (She also hired my wife's stepdad as her coach!)
How does this apply to the quirky world of screenwriting? Repetitive exercises will help you in music and sports, but they don't help when the muscles you need to be exercising are your creative ones.
But what will help you is the ability to keep working on a script when you're bored with it. Just because that first flash of inspiration is over doesn't mean you get to send your script out -- or not finish it. There is such a thing as overwriting a script, and you can't make a living if you're never willing to declare a script to be as good as you can make it. But most scripts fail because the writers weren't willing to keep working them till they were. Is that the best joke? Is that line of dialog as distinctive and character-revealing as it can be? Is there a way to make this scene play without dialog? Can this action sequence also reveal a plot point or a character point? Can I do something in this action sequence that I haven't seen in any Michael Bay movie? What if I changed this plot twist to something else -- what's the best thing I could do here that isn't what I already did?
And, most importantly, before you even start writing: have I told my screen story to so many people out loud that I know it off the top of my head, and every scene seems to come in the right place, and my story keeps my listeners enthralled, and I can't think of any way to improve it?
That's what separates the pro monkeys from the aspiring ones.