Borrowing from other authors. Shakespeare rarely had an original storyline. A Midsummer Night s Dream came from Theseus and Coriolaneus came from Plutarch s biography of the ancient Greek hero. Jane Smiley took the storyline for A Thousand Acres from Shakespeare s King Lear and won a Pulitzer. Cinderella has been disguised and retold many, many times.
Gothic novels are of that same nature.
Jane Eyre , Rebecca , the movie Working Girl . It can come from a personal event, family history, something that happened to a friend, or newspaper headlines. But the most original material will come from personal experience. By this they mean that the main subject or essence of the work can be clearly exposed in a few words. Think of ways to express your idea so that it is immediately understandable.