If you’re familiar with Blake Snyder’s Save the Cat story plotting method, you’ll start your story with the Opening Image, the first “beat” in your story. Snyder’s final beat is the Final Image, which relates to the Opening Image.
A tip: in your first draft, don’t worry about your story’s beginnings. Too many writers spend days on a “great” beginning. Usually this wonderful beginning doesn’t get used because the story changes as you write it. Work on your beginning in your second draft.