Chosen for Service: The Call
The story begins with your hero going about his regular routine. He may be content with his surroundings but something is off balance or missing of which he isn't aware. The call to the quest, usually from a wise mentor figure, disrupts this routine and often points to the thing the hero is lacking. At the beginning of "Star Wars," for example, Luke Skywalker longs for something greater than his monotonous life as a farmer, until Obi-Wan Kenobi calls him to become a Jedi. In your story, brainstorm an internal conflict your character might have, and think of how the quest he'll pursue could follow that issue.
Initial Insecurities: The Refusal
No matter how much your hero desires change, the risk of abandoning his comfort zone often is too great. Despite the reasons the mentor gives for why the main character must take up the quest, the hero usually refuses the call at first. In "The Hobbit," Bilbo Baggins initially is unwilling to leave the comforts of his home to go on Gandalf's dangerous and unpredictable adventure. Think about the character in your own story and consider what fears he might have about going on the quest. Brainstorm what past experiences or hardships initially could keep him from agreeing to go.
The Journey Begins: The Threshold and Descent
Eventually, something happens that compels the hero to accept the quest. It may come in the form of a threat to his values or family, as in "Star Wars," when storm troopers kill Luke's aunt and uncle. The hero often receives special abilities or gifts and has companions to help him on the journey. For example, in "The Lord of the Rings," Frodo's best friend, Sam, is his primary helper on his quest to destroy the ring, while Luke receives the lightsaber from Obi-Wan. Brainstorm characters, totems or objects that could provide your hero with assistance as he enters uncharted territory.
Into the Abyss: The Trial
In this climactic portion of the plot, the hero must come face to face with the object of his quest and confront the greatest danger of the story. Often, he must face this episode of darkness on his own with the quest as his sole focus, no matter what the sacrifice. In "The Wizard of Oz," Dorothy's trial occurs when she's imprisoned in the witch's castle and throws water on her. In your own story, think about how your character might respond to his intense confrontation and what could motivate him to continue toward the object of the quest regardless of his fears.
There's No Place Like Home: The Return
After overcoming the dark forces and meeting the goal of his quest, the hero returns to the home he was reluctant to leave and sees it with new eyes. Having been transformed by his journey, he brings new insight or wisdom to the people he left behind, or even feels frustrated by their inability to see what he now sees. Dorothy returns from Oz with the knowledge that "there's no place like home" but is upset that no one believes her experience. Consider how your character has changed as a result of his journey and what these changes might mean for his relationship to home.