When I start a new story, one of the first things I try to figure out about a character, before I know their hair color or even their name is what is their problem?
Figuring out your character's problem will take you a long way with your story. It's the basis for your character arc and internal conflict and quite possibly that Deep Dark Moment, too. Plus it will help readers identify with your character because he/she isn't some perfect paragon who needs to be knocked down a peg, but a flawed fellow creature with baggage, hang-ups, issues and hot-buttons...just like us!
To really make the flaw believable, I like to dig into the character's back story. Usually I try to make the flaw a part of their personality, which readers might subconsciously expect from this type of person. Since I always explore my characters' astrological signs to flesh them out, I tend to draw flaws that are common to those signs (or I pick the character's birthdate based on the flaw). So my Scorpio hero will have revenge issues. My Leo heroine may put pride before love. A Capricorn may have trouble expressing passion. The character's cultural background can play a part here, too -- a repressed British hero, for example, or a spitfire Irish heroine with a penchant for trouble.
To intensify the problem, I give the character a childhood backstory geared to play on the personality trait. Most of our baggage has roots in those impressionable early years. In my fantasy novel The Destined Queen, my heroine just wants peace and quiet -- a Pisces trait. During her childhood, her country is tight in the grip of ruthless conquerors, making her long for peace and security all the more.
I usually reinforce the problem further with a recent event that plays on the characters' deeply ingrained insecurities. I get a little impatient with a hero who thinks every women is untrustworthy just because his mother abandoned her marriage. But if his first real love also broke his heart, I'll buy his wariness.
Did I mention that not just any flaw will work for a story hero? In a romance, it's vital that your hero's flaw prevents her from forming a lasting relationship. That's where the internal conflict comes in. In a fantasy, a flaw that makes it extra difficult for the hero to acheive her goal/quest or task is a good one. Like Maura's longing for peace -- she's not going to get much peace searching for The Waiting King and helping him liberate the kingdom. So she is forced to confront and overcome her problem.
Finally, to help me shape my character arc (which often shapes my plot) I consider what growth or change the character needs in order to overcome their flaw. What Life Lesson does he or she need to learn? In Maura's case, she needs to learn that freedom is too high a price to pay for peace and that she is capable of greater strength than she ever thought she possessed.
Don't start hyperventilating, pantsers! I don't always know all these things at the outset of my story -- at least I didn't for some of my earlier books. Quite a bit of it came together as the story progressed or I was able to beef it up in revisions. Now, knowing how vital it is to my stories, I try to get it straight in my mind before I start, even if it's the only thing about the story I do figure out in advance.
Does all of that make sense? Need a few more examples to get the gist of it? Well, it just so happens I have some. Have a look at this handout on Character Flaws. It will walk you through the flaws for characters from several of my books and hopefully demonstrate what I mean. If you still don't quite get it, think about a character from one of your favorite books or films and see if you can identify these elements of that character's problem.
I hope a better understanding of character problems will leave you with one less problem when it comes to writing your manuscript!