Don't plot your story to death
Once you get commissioned to write scripts, things like proposals, exposés, treatments in every size, shape and form become the norm. In all of that, don't forget the muse and the free-wheeling flow!
Being commissioned means that someone’s putting up the dough - and that someone rightly wants and expects assurance assurance that the money's well spent. The time working on exposes and treatments is necessary, but it isn’t usually a whack of fun for the writer.
I've had the greatest bits of unstructured-free-flowing-anything-goes kinda fun with spec scripts and, on one rare exception, with a commissioned gig. As for spec scripts - heck, if nobody's on your back to deliver something one way or another - roll with it! All you need is your basic plot idea (and you'll know the genre, hopefully), your protagonist, your antagonist (plus needs, wants, obstacles - you know the stuff) - and off you go.
For me, personally, the most wonderful moments in screenwriting are the ones when you don't know everything beforehand. When you truly live with your characters and you just write down what they do and say as you accompany them on their journey. I've laughed and I've cried when non-plotted things suddenly happened - had to happen - because they came out of the story, out of the truth of each of the characters - totally honest, just there, live. Pure bliss. I've come across a fitting quote by writer Paul Theraux:
“It is fatal to know too much at the outcome: boredom comes as quickly to the traveler who knows his route as to the novelist who is over certain of his plot.”
Well, I wouldn't go as far as to call it fatal - but the man's got a point! As mentioned above, I've also had this experience once with a commission. Unbelievable but true - I pitched an idea, the network loved it. Next they said "the contract's on its way" and "we don't want a treatment, unless you want to do one."
I couldn't believe my ears. Of course I did a vague sort of treatment for myself - but when I had the direction, had all the important bits sorted out - I just let it flow. I had so much fun - coming up with the weirdest things, twists, turns, dialogue (just to give an example - I wanted one of the cops investigate to a tree trunk for marks in the middle of the night - and there I wanted him attacked by an owl. The my surprise, the director and the network responsibles loved it and it made it into the final film).
… And here's the punchline - the owl and all of the other very unusual stuff not only made it into the film - it also led to the film being Grimme Prize (Germany's top TV honor) nominated. I wish there were more such free-flowing experiences in my future - alas, unless I write specs - aka on my own dime - I don't expect to be in for a lot of uncharted script journeying.
But if you're a fresh writer and you write specs (and you better be writing specs!), you have the time and the passion and you crank them out - please, please do not plot your passion/weirdness/oddity/originality to death. Get the main points clear - then dive into that world, hold on tight and enjoy the ride!