If you're reading this and you haven't competed a feature length screenplay yet, you are still in Munchkin land. By no means does this equate to you being a bad person (or small in stature for that matter). You can live quite happily in the Land of Oz for a very long time. But if you're serious about becoming a professional writer, only when you have completed the first draft of your first screenplay does your journey begin.
Up until that moment, everything is still just a fantasy, but when you print out that first script, you have done it. It's tangible. You are now officially a writer, and the very act of completing something is your entrance into the real writing world.
Now, just because you complete a screenplay, however, doesn't necessarily mean you have executed quality writing. Your first script will probably be quite bad, embarrassing even, but that's because it takes ten years to have overnight success and a lifetime to become a master craftsman. Writing itself is what teaches writing.
But if you've finished that first draft, you have what it takes to continue, and you're probably hooked, slowly discovering that the real writing world is tough yet full of wonder. There's no limit to how far you can take that rabbit-hole, but there are three key ingredients that will aid you in your journey:
1.) A Writing Schedule: Treat it like a job and write everyday.
2.) Writing is Rewriting: Don't get married to your early drafts.