I've been thinking on this subject some more since last week, especially as Lucy (Bang2Write) Hay obviously didn't get what I was trying to say.
I WASN'T saying you should take examples from your life and force them on your characters essentially turning them into bastard versions of yourself. What I WAS saying is you need to refer back to emotional times in your own life to better understand the character you are trying to write. Let me try to make this crystal clear.
EXAMPLE: Your character is a teenage boy who doesn't relate to his mother, putting him on a collision course with her.
Go back and look at instances in your own life where you didn't get on with your mother and explore how you felt and how your actions helped or hindered that relationship. Then pick one really traumatic example, make it ten times worse and remove yourself from it, putting your character in there instead. Role play your character through that example from your life. How would your character have reacted differently? They are not YOU and will bring their own agenda to the situation. Remember it's not about imposing your life on your characters, it's about exploring your characters using examples in your life.
By doing this I have found it helps me to understand my characters better, by becoming them and exploring incidents in my life through their eyes. By the time I do this I already know who my characters are, this is not about development after all, this is only about getting into your character's head as you get ready to write your screenplay.
I hope that's clearer.