You have a luscious, compelling, thoroughly addictive story idea for your novel. You know how the novel opens--perhaps with a dream, which was Anais Nin's advice to a friend. Or perhaps you're starting with an explosive burst of action or with an immersive interior monologue.
You know your story's end, whether it's a tragic failure, a death, a marriage, or some other happily ever after that will satisfy your readers' sweet tooths. And you've written a good outline that will serve as the architecture for the middle, holding up the story and giving it coherence and structure. So now what?
Now you want to shape your main character so that he or she is a three dimensional human being. 
To pull off the herculean task of leading a reader through a few hundred pages of a book, that character has to be magnetic. Here are five questions to ask your protagonist, and the answers will lead to a fully fleshed out person who captivates your readers.
- What do you do, and are you good at it?
Americans always want to know what someone does for a living. Increasingly, because of the global economic situation, readers all over the globe are curious, how does this character support herself? The answers yield important information.
If she's a doctor, your character will be capable of grueling hard work, study, sleepless nights, and years of delayed gratification while she pursues a medical degree. Maybe she's a dedicated, selfless internist who volunteers in an Ebola clinic, or maybe she's a plastic surgeon who works four days a week and plays tennis every Wednesday before getting her nails done. It's one kind of person who chooses one path and another who chooses the other. Or say your hero is an accountant so he's good with numbers. He's careful, precise, and painstaking with details. Or maybe he's an inept accountant, and that's very telling!
This question helps create a backstory for the character. When she says that her happiest time was walking out to the backyard with her mother and seeing a spider web glimmering with dew in the morning sun, she's telling you something about her primal relationships as well as her appreciation for nature. Or if he says that his happiest moment was hitting a home run with bases loaded in Little League, then he's also talking about his competitive spirit and his desire to perform well. Whatever anecdote your character relates to you will reveal something important about who he is.
Real people are scored and sanded down and polished by failure and tragedy. Real people have regrets. When you delve into this part of your character's psyche, the part that has done things he or she isn't proud of, the part that has been shocked by betrayal or overwhelmed by misfortune, you get into the juicy kernel of truth at the heart of the human condition. You get a real person.
This question goes right to the heart of your story, of course. The action itself revolves around the character trying to achieve something or avoid something, whether it's to rescue a child, find a lost treasure, make a million dollars, arrive in the Emerald City, steal a fortune in gold bullion, or rescue a naughty billionaire with a penchant for kink. It's the story itself. However, there are usually two levels, the concrete and the intangible.
Your character may be trying to save someone, but in a good novel, there's usually more to it than that. If she succeeds, she'll prove something to herself. She'll know she's strong, or she'll find her inner wisdom and maturity, or she'll achieve redemption. He'll find the peace he actually needs rather than the revenge he seems to want, along with the gold bars. Maybe he, metaphorically, finds himself--his disowned and projected self--when he identifies the serial killer and solves the case. So this question is about probing into your character's motivations. Motivations arise from the essence of self.
These five questions will lead you into an enhanced understanding of the human complexity of your protagonist. Your understanding will inform the writing of your novel and give added depth and dimension to the characters and plot. You'll have set yourself up for that delicious moment of success that happens when a reader says, "I couldn't put this book down...."