Allow me to offer you an example: If you met a new friend, odds are you wouldn't grant that friend your trust until you knew them well enough, right? Well, the same goes for your characters. And just like that friend, the more time you spend with your characters, the more you learn to love them. The more you learn to love them, the more you care about their wellbeing. The more you care about their wellbeing, the more you care about how they handle their dilemmas (and all good stories need dilemmas).
There are a lot of authors nowadays that churn out story after story, self-publishing them, and the lack of attention they put in to the development of their characters comes through—the flimsiness shows. Stories like that are what I think of as 1-dimensional. The story itself has no backbone. It's fluff, and the reason being is because the characters are merely there for the purpose of moving the story along so a writer can self-publish for the purpose of hoping for sales (of course if the book is no good, you can probably say b'bye to sales). But the characters are what make the story!!! There is no story without characters!!
If you love your characters, odds are readers will, too, and they will give a damn and be enthusiastic to read about them to find out how they handle this or that situation, or how they react to circumstances. Once again, and I can’t stress this enough, if you care about your characters, your audience will care about them also.
I know it's hard, but spend time with your characters for a decent amount of time. I lived with mine for three years before I decided to write the first story in my trilogy. My characters are no longer an extension of myself, but they are their own entity--okay, with the exception that they do what I want. But the thing is, despite having them do what I want, I now wonder how theywould handle a situation as opposed to simply deciding on what I want them to do and throwing them into predicaments and makingthem dance through it. I labor over how so-and-so would maneuver through obstacles--it's no longer how I would do it or howI want to make them do it; It's all about the personality I created for them and how that personality will play into their situation and cause them to react. I don’t decide how I want them to behave, I take the time to wonder how they would handle the predicament I have put them in. I know my characters so well that I know what they would and would not do. If I come up with a way to resolve an issue, and I know in my heart that that’s not how my character would go about it, I nix my idea and figure out another resolution.
When your characters come into their own it shows--it projects from the pages and onto the reader. I realize it's tough to sit around thinking on and considering your characters, especially if you're keen to start writing, but in the end it's so completely worth it!
My characters are now like family to me. Of course I realize they do not exist outside of my head, but they do exist, and I have to consider their feelings and emotions just like I have to consider the feelings and emotions of my friends and family. If I don’t consider the personality I have developed for my characters and have them solve problems willy-nilly in order to move past an issue, then it becomes inherently clear (even to readers [who pay attention]) that it is, well, out of character for them.
My characters are just as important as the story I want to tell—without them, well hell…I have no story to tell!