Okay this took me embarrassingly long to figure out but, your character needs a thing they do that has nothing to do with the plot. A specific, weird, small habit. She counts stairs. He can't throw away receipts. She reorganises the fridge when she's anxious. It doesn't matter. It doesn't go anywhere. But the moment you give someone a habit that serves no narrative purpose they stop being a character and start being a person. And the reader can feel that difference immediately even if they can't name it.















