There is a school of thought that believes that the script that you are developing will have a direct relationship to your own life - more explicity that the transformational arc of your charcaters and the deeper themes of the piece are probably not so different from that which you need or are going though. Obviously this may not occur at the reality level (if you are writing sci-fi for instance) but at a thematic level in your life.
This is a challenging thought. If you honestly stop and look at the projects you are developing and the way your life is going at the moment you will almost certainly see this relationship in action. If your material is dark what does that say about you as a person - are you maladjusted? Unhappy? Bitter? Transcendently but imperfectly in love? Welcome to your audience :-)
Thinking back to my first 'proper' play in 1996 I would say that there are themes in it which strongly related to my own life at the time. Ok, so it was a historic epic comedy vampyre piece, but if I look at it more objectively then I can easily see some relationships.
The most obvious one for me was that I wrote the Vampire as something of a neurotic who was prone to anxiety and what I can now identify as panic attacks - a problem that I had been having for the six months prior to writing the script. Also the heroine has an arc about validation of her artistic drives - she goes from being a amateur painter to a modernist master some 150 years ahead of her time. This was at a time in my life I was making the transition from actor to writer, so an arc about artistic validation is right on the money. Another big theme in the piece - that of prior land claims of the New Zealand land mass and the sense of ownership - was important to me as I was contemplating leaving NZ at the time (and did, I wrote the thing over six years and in three countries).
The scary thing is looking at the pieces I am writing now and figuring out what the relationships are... Very worrying indeed! Luckliy I am fundamentally honest and brave enough to write directly from my experience without getting to queasy about it. I think all writers should probably expect to be analysed quite closely at some stage of their careers - firstly in development, then in production and finally in marketing and by the audience.
After all we are sharing our stories - and somewhat arrogantly telling an audience to spend time watching MY one - so we must be in them somewhere. The trick is to get there first!
So I have been paying very close attention to the things that I am writing and I can absolutely say that they are about things that are happening to me. An extension of this idea is that writing is 'working out' the material your own life is bringing up. To anyone in denial about this all I can say is.... see you on the dole que. Scripts MUST have this fundemental energy about them, must be fired from within. The audeince wants authentic and real (which doesn't mean it can't be set on a space station 3000 years into the future). What I am saying here is that there is a journey, a richer journey, to be had in relaxing with and accepting the kind of emotional examiniation (and lets be honet, turnoil) inherent in allowing that this relationship exists.
You go on a journey as much as your characters, doesn't that make writing the best adventure you can have while sitting still for hours at a time?!