Writing fiction is like doing a jigsaw puzzle. You fit the outside pieces first, so you have a framework to fill in (your story premise and theme), then you start placing pieces in to build the picture (scenes, characters, events).
The picture emerges slowly, not as a whole, but with intriguing colors here and captivating shapes there (the backstory and the characters’ relationships, actions and emotions). That’s what keeps you wondering what the whole picture will be when it’s finished, keeps you working on choosing the right pieces and finding where they go in the framework. A little at a time: that’s what creates the tension that keeps readers reading.
Not all at once, but bit by bit, piece by piece, until at last the picture, the story, is complete. Choose just the right details of the backstory that will move the action forward as you develop relationships and emotions and write the action. Then your story will come together like a fascinating jigsaw puzzle that readers won’t be able to put down until they, too, see the full picture.