If you are writing narrative poetry, especially longer narrative poetry, it is best to develop the story with the same tools as are used in prose narrative forms. One of these is understanding and purposefully designing the conflict in the story.

A simple story will have one main conflict. A longer story-line might have all sorts of interacting conflicts. A conflict can be man against man, man against nature, man against the gods, man against some quality within himself (fatal flaw), nature against nature, etc. Choose your protagonist and antagonist, whether these characters in conflict are represented by actual human beings or not. The conflict is then the center point of the story.