Map out the logical sequence of events before you begin writing. Your beginning, middle and end of the story, and any events that happen in between.
Use one index card per sequence, and write them down. Number the cards so you know which order they go in later. This will allow you to go over the events in the story in your mind before you start writing.
Write the first sequence of the story that you recorded on index card one. Introduce the main character and setting.
Use the second sequence to establish the action of the story. This could be an obstacle the main character has to overcome, or even another person, known as the antagonist.
Show your character working to overcome the obstacles in the third sequence. How are they getting around it or going through it? This is a common place to interject main plot points and action.
Establish a climax, where your character overcomes the obstacles. This is the climactic sequence in the story.
End the story. In this sequence, you will want to wrap up any loose ends left in the previous sequences so your readers experience a sense of completion. Once you've got the basic sequences written down, go back through and strengthen things like characterization, theme and setting.