There's a piece of writing advice I see or hear a lot: don't submit a story or script before it's ready. This is good wisdom and should be observed whenever possible. Of course, if you're on deadline and have to submit something, you have to submit. But the rest of the time, you have a choice whether or not you send your narrative out into the world.
So: if it ain't ready, don't let it go. Fine enough - but how do you know when it's ready? Every story, every script can be improved in some way. Let go of the fact your narrative is not yet perfect. It will never be perfect. It doesn't need to be perfect, it needs to be ready. But too many writers press send before a story's ready. I've done it myself.
Why shouldn't you send stories out before their ready? Because underdeveloped scripts make you look like a tool. You might only get one chance to impress a new contact, a potential employer. Send them an 80% ready narrative and they'll see the flaws. If your story isn't ready, chances are they'll think of you the same way. Opportunity wasted.
After you've forged a working relationship with an agent, editor, development executive, script editor, director or producer, then you can get away with sending them material that's not quite ready yet. A fully developed project takes months or years, and that's a lot of work only to be told they've bought something just like your narrative.
When you're already working together, it's easier for you and them to have early conversations about new stories and ideas. Saves you time and effort, enables them to get involved in the development process. They feel a kinship with the project, and that's useful to further the relationship. But if you're there yet, tread very carefully...
So we're back to that question: how do you know when a story's ready? Alas, there is no easy answer. The more you write, the more experienced you become. Hopefully you develop a gut instinct that tells you when there's vital work still to be done. It's a nagging voice at the back of your head that mutters, hmm, nope, it's still undercooked, bub.
If you lack the confidence to listen to your own storytelling instincts, ask people you do trust. Get feedback from three different folk. Persuade them to read your script and hurl questions at you. You don't want solutions, how they would fix the problems they perceive. If they only ask questions, you have to find your own answers.
Why three people? Because one person's opinion is just that - opinion. If two out of three people have a problem with a part of your narrative, it's worth reviewing. If all three react, you definitely have a problem. Your story or script isn't ready, it needs rewriting, rethinking or sticking in a drawer until you have some objectivity about it.
The more you write, the better your storytelling instincts should become. Just as a pianist improves with practice, so does a writer. You find your own rhythms, the methods that work for you. And you learn to listen to the little voice in your head telling you whether a narrative is ready to go out into the world. That's how you know. Onwards!