Novel Writing Basics Week
What is a Character Arc?
A character arc is how a character changes from the beginning of the story to the end. These aren't just physical changes, though those might happen, too. These are changes that occur because after your character has gone through whatever the story entrails, s/he can't (or at least shouldn't) be the same person afterwards. Characters might mature. They might become more selfless. They might learn to have fun. They might make a friend. They might learn to let someone go. All of these are character arcs.
Why Are Character Arcs Important?
Reading is a huge time investment, but one of the reasons we keep doing it is that satisfaction we get at the end. We love that feeling of closing a cover and thinking, "That was worth it." If a reader finishes a story feeling like the plot was interesting, the writing style was good, but overall the story doesn't seem like it went anywhere or had a point, that may be a sign that the protagonist lacks a character arc.
Character Arc vs. Plot Arc
The physical plot arc should not be a separate thing from the character arc. Ideally, both should come to their climax at the same time. Pixar is a master of this. As Riley is about to shut down emotionally, Joy tells Sadness to take control. In the final battle with Muntz, Carl gives up his house to save his friends. When the humans are about to capture a whole lot of fish, Marlin lets go of Nemo's fin. In the middle of the story's worst crisis, your character finally grows into the person s/he needed to be and wins the day because of it.
Getting Started
Find your protagonist's personality flaw.
Deciding how your character is going to change is difficult and requires getting to know your character very well. All authors get to know their characters in different ways. Some of are us "pantsers" (i.e. we write by the seat of our pants). We need to sit down and write a few thousand words of the protagonist's story without having a clue where it's going in order for that character to become fully realized in our minds. If that's the case for you, write those words. Get them out. But remember they're an exercise in understanding your character. If you have to trash them later, that's okay. You're a pantser. This is kind of your thing.
Others of us are planners. No way will we put pen to paper before knowing all the details. We might get to know our characters through filling out detailed profiles, taking walks and thinking about what conversations they would have, and maybe even drawing pictures of them.
Your goal in these exercises (whichever work best for you) is to discover your protagonist's flaw -- what needs to change over the course of the story. Keep in mind that flaws are things about your character's personality that aren't good and that could change if your character wanted to. Having no friends because other people are jealous is not a flaw. Physical traits are not flaws. (They may be an intricate part of your character and shape how s/he perceives the world, but they are not flaws.)
Once you know who your character is at the start of the story, you can envision who s/he will be by the end of it and start working towards that goal. If you "get to know" your character and find that s/he has no real flaws, back to the drawing board with you! 
Getting Going
Let your character's flaw change over the course of the story.
Character growth doesn't happen in a vacuum. Your character should not be going off by himself, thinking deep thoughts about how he needs to change as a person and then marching back out with his personality flaw gone. If fact, most characters will not even be aware of their flaws at the start of the story. The first few steps towards change might be simply realizing that "hey, other people think differently than I do" or "maybe there's ways to accomplish this besides the way I've always done it." Then, little by little, characters start to change their behavior. They will probably fall back on old habits plenty of times. That's okay. That's how change happens.
The plot arc should not halt in order for character growth to occur. In fact, the plot arc should drive the character's growth. Your immature character might be put into a situation where his/her childish behavior gets people in trouble and has to face that fact. Your stiff, humorless character might be in a spot where a little lightheartedness could have really helped. Whatever exciting adventures you have for your character to go on, always look back on the character arc and think, "how are these events going to help my character change?"
I'm a math person, and sometimes, I write percentages on my plot arc to mark roughly how far into the character arc my protagonist should be. For example, halfway through a story about a cyborg learning the value of emotions, she might have a divided, 50/50 opinion on them. She's made progress, she's still got a while to go. (If putting percentages on your novel outline sounds like something that would drive you insane, don't do it. I'm a firm believer in searching for the method that works for you, not forcing yourself through something you hate because it worked for someone else.)
Putting it Together
Depending on how you write, you might have that big climax of your story already planned. Or you might not know it until you write everything that comes before. Whenever you discover it, see how you can work the climax of your character arc into the same scene. Have your character do that one thing s/he never would have done at the start of the story. Get the audience cheering, crying, or both. The beauty of human beings is that even when we really screw things up, we can still grow and change. Let your character do the same.
Best of luck and happy writing!
