I'm reading Janice Dickinson's shockingly candid autobiography
No Lifeguard on Duty, and I find it striking that as soon as she started getting to work with top photographers, she started studying photography. Taking pictures, running them by the photographers she was working with, trying to improve her work, taking shots of the other models she was with.
That's how you get to be a supermodel.
When I was at film school, one of the classes I learned most from wasn't in film school. I studied Meisner Technique with Joanne Baron. I was not trying to become an actor -- Goddess forbid! But I was trying to learn what acting is like from the inside. This helped my directing some, and my writing more. Training as an actor helps you act the characters who are speaking in your scenes. If you act them, it's easier to write motivated dialog -- and short, heartfelt dialog at that.
The other class I learned most from was Richard and Barbara Marks' editing class. I took it three times, the first for credit, the next two times auditing. Richard Marks has been nominated for an Oscar for editing. (By now he may have won one, I didn't check.) I learned how to get into scenes late and out of them early. I learned how to end on a movement that propels you out of the scene and come in on a movement that draws you into the scene. The parallels for writing are not too hard to feel.
My actual screenwriting classes -- well, I got a lot of practice writing screenplays. I may be a particularly dense student, but I don't think I've ever had a breakthrough as such as a screenwriter, unless you count life-changing experiences like moving out of LA and getting a divorce. Probably the most valuable experience I've had as a screenwriter has been writing my two screenwriting books -- you learn a lot by explaining yourself.
Often coming at the problem head on is the least helpful way to get at it, as generals have had to re-learn in every war since 1861.
Learn from the other.