"That’s the question I’m most often asked by writers just starting out. Here are my top tips:
1) Put it away. Let it gather dust for a few weeks, then take it out, brush it off and get your red pen ready. Do that several times until you can’t make it any better yourself (or you’re going barmy, whichever comes first).
2) Ask an expert. Get the opinion of someone else, family and friends don’t count, unless they’re experienced writers, directors, producers or script editors. If you don’t know anyone in the industry, then have a look online at some of the experienced industry professionals offering script feedback. Don’t be lured in by the one with the jazziest website or the lowest rates, but do your homework."