Screenwriter Ben Hecht said, "Anybody with a good memory for clichés and unafraid to write like a child can bat out a superb movie in a few days."
I disagree that screenwriting is easy. But starting with clichés is not a bad place to begin. Start with the cliché, then twist it, throw it out, do the reverse, combine two cliché's in an unexpected way. For example, the interrogation scene in The Matrix is a cliché UNTIL we and the character realize we have no idea where we are and what this is.
Write like a child - meaning write with abandonment, without self-censoring. Write for the joy of it, for the fun of it, because you're amusing yourself. THEN you'll fix it, mold it, turn it into more "adult" fare. But when you start yes, write like a child.
So screenwriting is hard, not easy, but the approach of beginning with clichés and beginning as a child would begin is spot on.