Years ago, I attended a screenwriting course. It was over three or four Saturdays (can't remember exactly now) and although we did watch a movie or two, mostly the lecturer talked and gave us handouts and homework. At the time, I thought I might try my hand at writing screenplays. I'd written a play (a teen rock musical with a composer), a bad movie script, and dabbled a bit, but I knew I needed to know a lot more before I could have a serious try at it. So I went along to this course.
I couldn't tell you now (without going back to my folder of notes, because I never throw anything out) what I learned about screenwriting in terms of formatting and opportunities and stuff like that, but I have never forgotten the work we did in that class on character psychology. It was the first time I'd ever worked hard on character motivations in terms of who they were inside their head and why. Abandonment, fear of intimacy, abusive parents, alcoholic parents, power plays, control freaks - I think I learned more in that class than I've learned anywhere since.
Have I written a screenplay since? No. But every piece of fiction I've written has included, in some shape or form, psychological backstory and motivation. I now research my characters in terms of psychology and what makes them tick. I know that I need to make sure that how they are behaving right now is consistent with past events and the effects of those events. Today I was researching the effects on a male character of consistent physical beatings as a child and teenager. Something in my story wasn't adding up when I wrote about this character, and I realised it was because I didn't really understand where he'd come from, and what the long-term effects of that abuse might be.
I say might because if you read any psychology articles or texts, the first thing they'll say is that no one can predict the outcome of a particular experience. There are a number of factors that influence what might happen later. But it's very easy as a writer to say, "Oh yes, this happened and so later on he does this, and is like that" without actually verifying that a drug addiction (for example) is a possible/probable outcome later on. The character could have become a hitman! Or committed suicide. Or suffered anxiety attacks and withdrawn from the world. But you need to know what the range of possibilities are.
So this screenwriting course introduced me to how to create psychological depth in characters. Great stuff! Writing short stories for adults over the years has taught me how to write tightly plotted, pacy chapter books for kids. Writing poetry has taught me heaps about imagery and metaphor, and using the best words in the best way. Writing radio plays taught me lots about strong dialogue. Studying a unit at university years ago on performance, that was mostly about how actors fill up the space on the stage, taught me a huge amount about action, dialogue and pacing.
I think if you want to write novels, don't limit yourself to just learning about how to write novels. Learning how to structure a screenplay will teach you lots about plot and cause/effect. Not to mention dialogue. Watching movies will teach you about showing and telling. How is that actor showing distress? Puzzlement? Embarrassment? Go and write some poems. Write lots of poems. Read lots of poems. Discover what language is capable of, if you use it effectively. And yeah, don't forget the grammar and punctuation stuff. That'll teach you how to write a sentence that says what you want it to, create the effect you want for the reader, without being obscure, overblown or confusing.