I think writing convincing characters, above all elements of storytelling, is a process that encompasses the focus of a writer. Over time the stories that we know have changed. Before, say in the middle ages, stories were really binary, generally serving the purpose of warning their hearers away from tempting lifestyles. Before that stories were transgressive. They would tell the hearer about a reality that was, and the reader's job was to either accept of deny if such a thing was possible. Early Christianity falls into this realm with St. Paul promulgating not a religion but a story of a different reality. Today things have changed. No longer do we write stories with interesting plots, but interesting characters.
When I was near the end of my second revision of Spirit of Orn the thing that made me most wary about it was my characters. In it there were still characters that I didn't know what would say in a given situation even by the end of the book. Obviously, the most ideal thing is looking at a character and saying, "Oh, Steve would say that," or, consequently, "Sharon is a vegetarian, and a ponce. She could never think that!" If only it were that easy. I think as I get better at storytelling I can begin to streamline my work. As of right now, I'm going with "Third time's the Charm!"
But can we avoid this?
I think so. There's a lot of prep and guesswork that goes into making a book at first, but then once all the pieces are assembled, you can begin to get a grasp on what you are really writing. At first, Spirit of Orn was a parody, but as I got farther into the project I found out that it was really a analogous memoir. After that, everything just kind of fell into place. So really knowing what genre you are writing can be helpful.
Another thing is that if you don't know what your character is really like, really get out some markers and crayons and draw your cast onto a large poster paper, and ask yourself, "If I took two of these characters out of this story, would they make an interesting book?" When you think about it, most conversations in books are between two people. Rarely do you have a conversation larger than three people. The reason why this works is that in two person conversations yourself and the reader are naturally going to see how the characters complement one another. If you are married this will make sense. Before I got married I had a psyche evaluation with my bride to be and we both found out that our personalities complement one another very well. If you are writing a book, and your characters are all more or less the same person then you are going to have a really boring book. So in my book I might have a character who is the son of another character. The son is boisterous and rowdy, while the father is measured and practical. While the father will still be rowdy in some respect, because he too was once young, age and maturity will develop him as a character.
There's a home brewer in my book that's boring...
I thought about this the other day. Generally it's easier to write interesting primary and supporting characters because they are involved with the plot, but if there are one shot characters that pop up, it's hard to think of them more than set pieces. There's a really interesting book called The Name of the Wind. written by Patrick Rothfuss. He is known for the creation of fantastic one shot characters and I think what he's doing right in his craft is making them first, empathetic. Then, he makes them intimately connected to the character's journey in some way. There's a character in my book for instance that is an embittered woman that is a feminist now because of the way a supporting character in the book treated her. Before in the book she was just a bitch. But people are bitches because something caused them to be a bitch. Therefore I dug a little deep, and was rewarded for it.
I hope these help. After three years of writing a novel I imagine my second one will be a lot easier to write. In the mean time however, my biggest hope is to spare you from saying, "Third times the charm!" Good writing should always just flow, never premeditated.