8. Read Your Dialogue Out Loud
This might seem like an incredibly simple tip, but many writers just don't seem to take notice - maybe because it seems weird or something to actually do it, or because they don't like the idea of somebody overhearing them speaking their dialogue out loud. But do it. Do it all the time, at the end of every scene you write. Read every single "finished" line of dialogue out loud and see what it sounds like to actually hear it. You might be surprised. I've written lines of dialogue that I thought sounded great on paper, only to end up saying them out loud and finding that they don't sound right. If you pick up a novel and read the dialogue out loud, more often than not you'll find that it sounds oddly clunky. Stephen King's dialogue works amazingly in his books, but on screen, it's usually terrible. Stephen King just isn't very good at writing dialogue in screenplays. It's a totally different style. My point is: if it reads good on paper, it might not read as well when it's being said by an actor in real life. Genuinely imagine that your dialogue is being said out loud by a paid actor; see if you can actually imagine somebody saying it in a movie. Sometimes you'll have to change a few words around, or maybe you'll have to rephrase the line entirely because what you wrote just doesn't flow quite as well as it did on the written page. Better yet, if you can find somebody willing to read through you entire script with you, seize the opportunity: when they stumble over certain lines or you see them struggling to get one of your sentences out, it probably means that your line is a dud. Have them try to them reinterpret the line in a way that makes them feel more comfortable - you never know, they could be onto something. If not, at least you've been made aware of it.