Comment by K_REY_C

Try the "writing excuses" podcast. Is not screenwriting, but many many of the same elements apply. Also, screenwriting is ultimately meant for the screen, so that intently means a collaboration with someone visual. Talk to people who will be honest with you, but only once you've finished at least a scene. Your idea, the thing you want to write, can get lost if you listen to too many people before getting it down and out at least once.