Do you often stop in the middle of a short story or novel and say, “Now what?” It might be because you don’t know your character well enough.
Put away your story and just wonder about your character. Daydream about her/him.
What is her biggest desire? Her magnificent obsession? What is a secret she carries inside that she doesn’t want anyone to find out? What is stashed away in the depths of her closet? What does her bedroom look like? What is hanging on her walls? What does she eat? How does she eat? Pick at her food? Wolf it down? What is her earliest memory? The funniest thing that has ever happened to her? The scariest? Something that will happen to her in the future? How does she react if she witnesses a theft? How is she different from you? How is she similar? How is she quirky?
Write scenes about these questions. They may never appear in your story, but you must know your character backwards and forwards so that you’ll know how she’ll react to situations within your plot.
Next, play the what if game. What if your character . . . gets in a car accident. What if she sees an animal hurt by the side of the road . . . what if . . .
You get the idea. And place her next to your other minor characters. Ask the above questions about these guys too. Know them all so well they seem like your friends that you carry around with you in your head.
When you think of your main character more than you think of your regular daily life, then you may be ready to get back to throwing her inside your story. And away you go . . .