Figure out how the parts work.
“It is perfectly okay to write garbage as long as you edit brilliantly.” – C. J. Cherryh
Editing is the work.
You cannot get out of it. This is why people in the business say ideas aren’t worth anything. The job of the writer is to hammer them out for everyone else. If you haven’t done that part, you haven’t done shit.
Just get it all down, then go back and fix it.
And fix it. And make it better. And fix it. Go work on something else for a while. Come back, make it even better. Writing 10 to 20 drafts is not uncommon.
The more you write, the faster you’ll probably get, and the less necessary rewriting should become, but everybody’s different. If you’re still outlining in detail at 150 scripts in, who cares? You do what works for you, as long as it sells. But, yes, it should get easier.
Don’t Try To Sell Your First Draft of Your First Feature.
As has been said many times, writing takes practice. Finish your first feature, then write something completely different. Then go back and look at your first feature… you won’t like what you see. The more you write, the more aware you become of your own mistakes, and the more effective you become at eliminating them from new work. So, when you “finish” that first script, put that shit in a drawer.
Don’t start calling Netflix Customer Service asking to speak to the head of development when you’ve just finished writing your first scene.
You will be competing with people who have been writing screenplays for 40 years, so you absolutely must bring your top game. Build a network of fellow screenwriters and swap scripts to exchange notes. You don’t have to take all their advice, but you also don’t want to be living in an echo chamber or only get feedback from people who just want you to be happy.