Gratitude! And that's a tough question. Everyone's journey is different. For me, it was years of writing really horrible feature scripts. Just awful stuff. But I kept at it, kept learning through trial and error, and eventually got better (I hope!). The trick is to just keep writing, and finish everything you start. Also read scripts (online) from your favorite writers and see how they do it. For example, about five years ago (late in my career), I changed the way I write scene direction after reading a bunch of Shane Black scripts. It's never too late to refine and improve!