Revised Essential Question

1. My revised essential question is: what is the best way to write a successful screenplay?
2. Defining terms seems a little difficult with my question because I interpret the question a bit differently. By 'successful' screenplay I don't mean one that makes loads of money - realistically that almost never happens anyways except for a few lucky hollywood hotshots - but successful to me is screenplay that people want to buy. And what I mean by 'best way to write' is as far as writing goes what makes a good screenplay? My answer will be in the writing of the screenplay. So what I am really asking is: what in the screenplay makes people want to buy it? Some people will buy a script because there is a name on it, but there are still others who sell their screenplays solely based on the screenplay... why do people invest in those scripts? I once heard that "most screenwriters get paid nothing, what makes you any different?" And that is precisely what I am looking for! What does make them different?
3. I think likely answers will be: new/unique storytelling, unique insight, witty characters, story/character driven stories, or an incredibly relatable story.
4. My greatest source so far has been my reading of real screenplays.. I have only read one whole screenplay BUT I really got a lot out of it. I am even excited to read more... the only thing is, I have been reading about working screenwritersin my research and there is so many depressing things to be said... like the fact that the majority of writers will be out of work this year, the average writer makes less than my father, hollywood is a shmuck, and to be quite honest with myself if there was a secret to writing screenplays that could be decoded in the greatest of all sreenplays then someone would have found it by now. I have helpful research but its discouraging as well.