Completing a large project like writing a novel or screeplay without any feedback is daunting. It's all too easy to start wondering whether you've chosen the wrong story or the wrong structure or even whether you're wasting your time writing at all.
However, asking for feedback too soon can be destructive as well. A negative respone can crush your spirit.
One solution is to get small servings of feedback on specific elements. For instance, if you're writing a thriller, you might discuss your villain with someone without having them read anything, or you might just give them the paragraphs that describe that character.
Ask them specific questions: What's their first impression of this character? What are they curious about? What kinds of action might they expect from such a person?
Discussions like this can help you see whether or not you're on the right track (that is, the track you want to be on) with elements of your writing, but without the usual negative effects of getting input too soon.
(You'll also find friendly and practical advice on writing your book or screenplay in my book, Your Writing Coach, published by Nicholas Brealey and available from Amazon or your other favorite bookseller.)