From the Getting Started in Writing Workshop:

How do you go about planning the plot for your story? One way is to use an outline. Opinions about using an outline as a plotting tool vary widely. Many writers feel constrained by an outline that is too detailed, while many others feel that a well-crafted, scene-by-scene outline�by taking care of plotting considerations ahead of time�actually frees them up to be more creative during the writing process.

How (or whether) you decide to use outlines will ultimately be a personal choice based on trial and error. But we think it's a good idea to start with some sort of plan, so we'd like to introduce you to one writer's plotting method, a simple, straightforward approach that should work for any type of story. It is called the "Triple-O method," described by John Nanovic in the 1945 Writer's Yearbook:

Plotting can be brought down to just three little words. ... They are:

1. Objective
2. Obstacles
3. Outcome

That is your story, no matter how you twist or turn it, or how you color it. Your hero sets out to get something [objective]. The obstacles that are in his path are the things that make your story. The outcome of his battle with these obstacles gives you your climax [and resolution].

The Triple-O method is particularly useful in plotting the short story because it helps you identify the one objective and obstacle your story will revolve around