When you sit down to write a story, you need to have a plot or pathway along which your story will develop. The trick is to make the plot unexpected so the reader walks away shaking his head saying, "I didn't expect that," instead of, "that was a boring story." Some people have the ability to think ahead and plan out what they want their main character to do, while others like me spend more time in the present. Since I lack this creative foresight, I need to actually draw out a flow chart that shows how one action leads to another. If I have a desired outcome, I will draw the flow chart backwards.
According to Tameri, you should be able to describe your plot in two dozen words or less or it is too complex. Since plot is also described as the conflict within the story, you can use the emotions around the conflict to enhance the story from a simple short story to a complete novel. For example a simple plot is two kids got lost and found a house of candy, which they were not supposed to eat. Hansel and Gretel provided us with so much conflict that most of us never have forgotten the childhood story.
Of course, practice is the key to developing a plot. One of the funnest ways of doing this is in front of children while you watch their faces reflect the emotions of your story along the path of your plot. You should try it sometime.