I believe that the best fiction is character-driven. Plotlines are of secondary importance, because if we don't care about the characters then the drama that unfolds around them fails to stir our interest. This division is really an artificial one, though, because within a good story the plot is an outgrowth of a writer's understanding of his or her protagonists' true natures. The adventure that beckons them is one that they need, or deserve, so the two are intertwined.
How do we hope to arrive at an understanding of our characters and their destiny whilst faced with the first blank page of a (hopeful) novel or story? The prospect is less daunting if we realize that we don't NEED to thoroughly know our heroes and villains at the onset. We need only a starting point and a glimpse from afar; or a first date, if you will. The rough draft is our "getting acquainted" period. We aren't married to our characters until the second draft, and even then we have recourse to literary divorce.
Allow me to describe two wellsprings where I'm wont to go to fill my buckets with character inspiration.
I'm writing this on halloween, a night when children and adults have license to dress up and assume adopted personas. Many are quite zealous about living out their alternate identities, which oftentimes contrast sharply with their everyday lives. Much of the fun of halloween is derived from the freedom we have to let our alter-egos express themselves for a night.
I am typically a quietly disciplined (albeit ambitious) writer and a doting father. But there's an inner showman in me who aches to be up onstage crooning and gyrating like Jim Morrison. My exhibitionist self loves heavy-metal, grunge, punk and psychadelic rock. He insisted that I make music a core element of my first novel, and even that I include song lyrics. In an opposite corner of my psyche there exists a geek who could easily spend days at the library or on the computer surfing the web. He made some unexpected and fortuitous contributions to my book including such characters as a chemistry hobbyist turned City Father and a diplomat and interpreter living within a tribal culture. Another character, a young woman with a passion for history and literature who also plays Pan-pipes, was the result of "collaboration" between these two secret selves of mine.
If you mine your psyche for alter-egos, you're likely to find that they have surprising stories to tell. Clues to their existence can be gleaned by examining your hobbies, your taste in casual reading and even your daydreams. Isolate these figures and give them a chance to speak their minds. Your pen hand may have trouble keeping up with them before long.
When we dream we travel through the landscape of our own rich inner world. Our deepest beliefs and feelings are personified and given voices. During the day our inner monologue operates constantly, and our thoughts sway us this way and that. We make myriad large and small decisions, and our motivations can be as varied as our choices themselves. Within our dreams, the collision of our thoughts and belief systems is enacted as an otherworldly drama. This inner play is intended to reflect our spiritual condition. Archetypal psychology has evolved the system of gestalt, wherein patients engage in active dialogue with figures from their dreams.
Writing can be a form of gestalt, with the poem, short-story or novel serving the same function as a dream. So the figures we encounter when we sleep can provide another rich source of inspiration for characters. Dream entities are akin to our literary creations; both represent parts of ourselves, and yet at the same time they are more or other than what we are. They receive the germ of their identity from us, but then they take off and evolve in unexpected direction - just as children will diverge from their parents' footsteps.
For this reason I believe that spontaneity is of utmost importance in any form of creative writing. I begin my novels or stories with only the barest sketches of my characters; and then I give them space to come into their own. You may find that your own characters will inevitably do this too, and your painstakingly-drafted outline becomes redundant by the third chapter of your book. So dip into your inner well for your initial impressions of who will be the main movers in your story. Then let them find their feet as you write.
I'll conclude the parenting analogy with this observation: we want what's best for our characters, but we can't plan their lives.