Finding the perfect plot is something which writers agonise about, but asking yourself a few simple questions will soon help you to tease out the germ of a good idea.
Girl meets boy, girl loses boy, girl wins boy back and they live happily ever after. Think of this corny old outline as the foundation of your narrative. The plot is the sequence of events through which you describe your story taking place. The way to derive a plot from your original idea is to keep asking yourself questions.
Girl Meets Boy. What is the girl like? What is the boy like? How do they meet? Have either of them had partners before and if so was it a positive or negative experience? What are their first impressions of each other? Is one of them more keen than the other? Where do they meet? Does the meeting go well, or is it a disaster?
Girl Loses Boy. What exactly has she lost? How far has their relationship developed? Does it have a solid foundation or has it been precarious from the start? How does she lose him? Does the loss come as a surprise or was it predictable from the outset? Is another person involved? What effect does the loss have upon her? What does she decide to do about it?
Girl Wins Boy Back. How does she achieve this? What odds are stacked against her to make it a challenge? Does winning him back occur in a single moment of realisation or does she conduct a sustained campaign? How has he changed? Why has he changed? What makes him want her back?
They Live Happily Ever After. Or do they? Are the auspices positive or negative? Is it a question of “be careful what you really want…” What is happy?
When you have answered all these fundamental questions you will have the basic elements of a plot. You then need to think about structure – how you fit all these elements together, but that’s a story for another day…