Think about what you want the main message of your story to be and if possible what you want to get your readers to think. Give your readers the feeling that they want to really think about problems, issues or ideas you bring up.
Structure your introduction so that it grabs the reader's attention. It should also make a point. The introductory phrase should be short and interesting, state a thesis and tell why the story is significant.
Write the main body. The main body can have as many paragraphs as you want, but it should have at least three. Each paragraph should cover one idea and follow a logical pattern. The easiest way to do this is to put the events in chronological order.
Sum up your narrative with a conclusion which is just as important to your story as the introduction. If you don't feel comfortable summarizing the idea of your story, you can end with plans for the future or a rhetorical question.