Follow the basic five-part plot structure. Start your story with exposition during which you introduce the main character, setting, and establish the conflict for your story.
Next move to the rising action. In this section gradually bring the central conflict to a point where your main character must take action.
Bring your story's conflict to its climax. This is the moment when the conflict peaks and reaches its greatest intensity. It can be an event as epic as the final battle of a war or as basic as your protagonist building the nerve to ask his love interest on a date.
After the intensity of the climax, you've reached the denouement (or falling action). Wind down your story and being tying up remaining loose ends.
Conclude your story at the end of the plot arc. Not all stories need to be concluded, however. You may choose to leave an open denouement, in which not all loose ends are tied up. This leaves the ending up to the reader's imagination.
Write a first draft from your plot outline. Do not be afraid to deviate from your outline. If you have a whim, run with it and see where it takes you.
Have an observant reader read your first draft. Ask your reader to point out places where the plot doesn't make sense. Find out what questions require answers that seem to be missing.
Use the observations of your reader(s) as well as your own thoughts to rewrite the story. Rewrite the story from scratch and see what new trends emerge. At this stage of rewriting you are still figuring out the plot.
Continue this process until you are satisfied with the form your book has taken. In subsequent rewrites, focus on word choice, phrasing, and other details to make your book the best it can be.