One of the most subtle tools I think the writer has to coerce to his or her side in this battle we call fiction is point of view. I keep reading everything I can get my hands on about it (henceforward referred to as POV) so I can know as much as humanly possible about the enemy. Ahem...I mean, the fabulous nuance available to me as a writer.
The current book on craft I'm studying, at David Farland's behest, is called Writing the Blockbuster Novel by Albert Zuckerman, and the author asserts that you are best able to write a book that garners a wide audience by employing a handful of POV characters...not one, not a dozen. His logic is if you give your readership an array of personalities to see the story through, and you're sure to make those POV characters different enough, different readers will glom onto different characters and hang with your book because of their favorite.
The trick I hope to figure out is how to make my POV characters fascinating in ways that cross over expectations. Of course, men are more likely to identify with a male character of a similar age as themselves...but how do you get them to identify with that female character I have interlaced in my story? How do you endear her to the male reader...going beyond perhaps just a sense of attraction, or an instinct to care for that character in a protective way? (Hold on one sec while I duck the hurled objects coming my way for making stereotypical generalizations. There's a reason those generalizations exist, you know...just sayin'.)
How do you encourage your female reader to invest in the grizzled once-war-officer turned slave? I haven't figured out yet how Brandon Sanderson has done it, but I have very much bought into the character of Kaladin in his Way of Kings. I have nothing in common with the character at all, and yet, I find in just a few hundred pages, I definitely care about what will befall him.
So it seems to me, the job is two fold. The author first has to get you to generally like the character in question. Whether that means you like the character because you identify with him, you admire her, or you simply can't help yourself (which is my situation regarding Tony Stark. I can't help but love him, even thought I feel sort of stained for doing so!) doesn't matter. You just have to want to see more of that fictitious person.
Then you have to feel the compulsion to care about what that character wants, no matter how far-fetched or outlandish. (On an unrelated point, another thing Zuckerman says sells books is larger-than-life plots and stakes.) If you as an author can accomplish these two goals, likability and "buy in," whether the character in question is an old man or a teenage girl will be secondary. The reader will keep the pages turning to find out what befalls their new friend.
So I open up the floor to you, readers: What factors help you invest in a character so you'll stick with him through hundreds of pages, perhaps lousy (though dramatic) choices, and unbearable peril? Add your comment below.