Decide on the plot arc and conflict of the story that you will tell. It is important to at least have a general idea of the sequence of events so that you can determine what the story will be about, even if you haven't yet determined the ending.
Determine the point of view that you will use to tell the story. Will you tell it from a first person point of view as if you are the main character? Or will you choose third person limited with a more distant narrator closely attached to one character and his thoughts and feelings?
Develop the details that you will include when telling the story. Make a list of important details for each scene and double check to make sure that each detail is relevant and does work either setting the mood or illuminating something about a character. You want your audience to experience the story, not simply hear a list of events.
Check your pacing. Do the events flow naturally? Is there a logical progression from one scene to another? Are there areas where the story moves too quickly due to a lack of detail or too slowly due to an overabundance?
Create a climax and denouement for the story. In the climax, the tensions will reach a fever pitch and in the denouement all of the story's conflict should be worked out and come to a resolution.
Determine the story's end and the change, if any, your main character has undergone due to his decisions and the events of the plot.