Give your mind as long as possible to come up with something original.
I tend to have an odd split in my mind: I tend to look at it as a writer and when the writing thing is OK and I'm happy with it, then I put on my actor's hat.
This is the extraordinary thing about creativity: If just you keep your mind resting against the subject in a friendly but persistent way, sooner or later you will get a reward from your unconscious.