For each of your main characters, you determine their Goal, Motivation, and Conflict. You come up with with a basic description of their personality (which for me is incredibly difficult), a Tagline (which could be lessons she needs to learn, or perhaps his personal motto), and then, you start in on determining what they want, what makes them want it, and what is keeping them from achieving their goals.
The amazing Debra Dixon came up with this shorthand in her amazing book called (oddly enough), Goal, Motivation & Conflict: The Building Blocks of Good Fiction.
One hint before you dive in - when you are working on this exercise, make sure your character's external goal is a concrete one. "World Peace" is a nice goal, but it's completely undo-able. Make it something that he can attain. Instead of World Peace, write "Obliterate X Terrorist Cell" or "Get President to sign X Peace Treaty on time and alive". For something less Earth shaking, try, "Buy childhood dream home" or "Open coffee shop in six weeks". What kind of story you have often depends on the antagonist's Goal.
For example, let me show you one of the GMC charts that Ms. Dixon uses in the book - Rick Blaine from Casablanca.
Rick Blaine
Description: Cynical Loner
Tagline: (lessons he needs to learn)
One person can make a difference in this world
Women in war must make desperate choices (think of the newlywed)
Goals: (what he wants)
External
- Keep bar open
- Punish Ilsa
- Get Ilsa and Victor on that plane
- Regain the love he had in Paris
- To do what's right in the world
Motivation: (because)
External
- Needs money and people depend on him
- Because she left him in Paris
- Insure her safety
- The pain of losing Ilsa has never gone away
- Daily, he sees what war is doing to people around him
External
- The French Prefect has all the power
- Punishing her puts her in more danger
- Victor has been put in jail
- Ilsa is married
- He must put aside his own happiness
Looks easy, doesn't it?
It's actually a difficult chart to fill out because you are constantly learning more about your characters and your story. The big part of a good character arc is discovering how their GMCs change from the beginning of the story to the end.