In striving to be loved or good or well-received, screenwriters very often write the script they’ve heard someone else write, without any regard for the characters with which they have thrown in their lot. This is a species of formulistic writing, and renders the screenwriter deaf to the possibilities of his/her own characters and their origins. Alas, the world of filmmaking is strewn with bad imitators of Tarantino, Woo, and others. Not that there's anything wrong with imitating the artists you love. Making experiments using the voices of others is a great way of learning how the language works (and plays), and can be of great benefit so long as you don't get stuck there.
Finally, it helps a lot if you actually have something that you passionately want to say. The search for voice is not successfully conducted when armed with thinly motivated enthusiasm. The quest is for much more than micro-drama. You need to be in love with something and then find characters whose problems, goals and plans dramatise that passion. When they care and you care, your audience has a chance of caring.
As for finding these characters to begin with — you don't find them to begin with. They have to be seduced into aurality... but here's a handy hint to get you started — for those who have ears, let them hear.
There is a terrific lot that can be learned about your characters by reading what you write ALOUD, particularly in the company of strangers.
Try this: Buy an all-day bus pass and ride the bus with your script.
Introduce yourself to likely looking passengers — ones that aren't likely to get off at the next stop.
Tell them you’re writing a movie; they’ll be interested.
Ask them if you can read a few pages to them. They needn’t comment.
What you hear coming out of your mouth will speak volumes.
What's needed is an audience, especially when the writer isn't discerning or critical enough, which most writers aren’t. If a crowd in a cafe or an auditorium isn't readily available, grab the first person that comes along. The bus is good cos you've got a "captive" audience. Anyone will do, but preferably someone who isn't a close friend, who will keep his/er mouth shut and not shower you with praise. Forget the praise. It's often little more than a hackneyed way of staving off the embarrassment of silence.
It hardly matters what this "audience" reaction is because if you've been listening to the script yourself as you've been saying it (aloud); you'll know instinctively which parts work and which parts don’t. You can HEAR it!
It's all there, right before your ears.
Check out Billy Marshall Stoneking's blog at BillyStoneking.blogspot.com.