Most writing "experts" favor a particular way of looking at plot, and will adhere to it for years or an entire career. That's all well and good, but its important to realize that any way of modeling story is just that -- a model, not the depths and living essence of story itself.
Problems arise when young (or experienced!) writers mistake a simplified structure for some deep and eternal truth. It's much better to examine several structures, see what their strengths and weaknesses are, and try to glimpse the truth they are trying to convey.
The actual "truth" of story is beyond any structure, but they all point in the same direction, toward that misty, hidden metaphorical mountain all storytellers have been climbing since the beginning of time. As long as we don't mistake the finger for the mountain, the structures can be quite useful indeed.
The worst story model that is at all useful might be" "It has a beginning, middle, and an end." Well, yes, but so does a piece of string.
More helpfully, try: Objective, Obstacle, Outcome. In other words, a character wants something, and something stands in her way. She tries various things to resolve the difficulty, leading to an eventual climax.
This one is even more useful:
Situation, Character, Objective, Opponent, Disaster. Using the classic James Bond film Goldfinger as an model (action films are good for this, because their structure is usually crystal clear):
Situation: When gold is being smuggled from England in large quantities,
Character: Secret Agent 007 James Bond
Objective: Is assigned to find out how it is being done. But little does he know that
Opponent: Industrialist billionaire Auric Goldfinger
Disaster: Is smuggling gold to finance his real operation, the destruction of Fort Knox with an atom bomb!
Can you see how this model helps to clarify the different basic aspects of your story? The hero must have a goal, and there must be forces in opposition. Moreover, the hero's initial goal and his ultimate goal may well change over the course of the story, as they grow to understand the situation more fully. A story structure like this one implies both internal and external motivations, and sets up a dynamic structure that almost writes itself!
The very best writing structure would be what is known as the "Hero's Journey" created by Joseph Campbell, and explored by anthropologists and writing mavens around the world. There are numerous interpretations of it, but in essence, it can be represented as:
1) Hero Confronted With A Challenge
2) The Hero rejects the challenge
3) The Hero accepts the challenge
4) Road of Trials
5) Meeting allies and gaining powers
6) Confront evil and defeat.
7) Dark Night of the Soul
8) Leap of Faith
9) Confront Evil and victory
10) Student Becomes The Teacher
This pattern automatically implies the yearnings, fears, obstacles, efforts, deep depression and exultation of actual human lives. This is the reason that this pattern, more than any other, is useful to writers both new and experienced. Because it mirrors our lives, a writer can most easily adapt her own understandings of life and the universe into her work. If you organize your work into this pattern, readers or viewers all over the world will instantly recognize your efforts as "story." Whether it is a "good" story will depend entirely on the skill and creativity that you bring to the task - the unquantifiable quality of "art" that is beyond direct description.
There are, of course, many other patterns, and an ambitious writer or student would do well to list several of them side by side, and analyze what they are saying. None of them are "truth," but all are useful fingers pointing toward that mountain.
Bestselling novelist Steven Barnes has lectured on story and creativity from UCLA to the Smithsonian.