Hey Sirius-
I've got some foolproof, can't miss advice for you on this one.
You say you haven't been able to finish a screenplay? Well, EVERY writer goes through this to some degree. It's largely a mental block though, and I found any easy way to overcome it.
First off- realize that as a successful screenwriter you will be be writing scripts constantly. Over the course of his career Robert Towne has written over one hundred. But most of those scripts will never be sold or produced. Doesn't meant they were pointless to write, just that they were stepping stones in between your other, successful projects.
Okay, on with the advice-
When it come to finishing your first screenplay the trick is- JUST KEEP WRITING. Doesn't matter if you think it isn't any good, or the dialogue is clunky or Angelina Jolie won't want to do it. Try to keep it coherent, but really, IT DOESN'T MATTER. Just get it done and put it in a drawer.
BAM- you are now a screenwriter. No more pressure. Now go write another script with a nice calm state of mind knowing that you WILL finish it, because you already have done it before.
I realize the idea of writing two (or twenty) screenplays seems daunting now and that first one is probably your "baby" but- get over it. If you want to be a screenwriter, well, you are gonna have to write. Speaking of which, why aren't you writing now?
