Outline of what will happen in your story. One way to do it is to think of your story as mountain, like this:
Beginning – Introduce your characters and the setting
*Start climbing – Something happens to your character to start the action.– a problem, a dramatic event, a mystery.
* Introduce more than one problem. Two or three work best to keep interest growing.
Resolution – The problem(s) get resolved.
End – The threads of the story are tied up.