Characters sometimes come out of thin air, or you can build them piece-by-piece. I recommend spending some time with and getting to know each one of your characters before you begin writing.
Write complete backstories for them, their passions and pains, their joy’s and sorrows; the details! The smaller the better, what is their favorite color/food…
You don’t have to use everything you write down about them but it will aid in the flow of your script as well as help you out of binds if you find yourself stuck at points not knowing what to do with them. Trust me it will surprise you.
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