I remember doing one interview for a blog tour where I was asked a question about the "everygirl" character. The question was, did I purposefully make Mel, the main character of Rain, very different from the "everygirl"? (If you need clarification on everygirl--I did--I found this to be amusing and helpful.)
My answer was, no, I didn't purposefully write Mel as pretty much the opposite of an everygirl. But while I see the value in such characters, that description could never. Ever. Be. Mel. So I never could've written her as an everygirl in the first place.
This ties into my Chemical X formula: defy stereotypes. Highlight traits of your characters--main or secondary--that contradict their role or even other characteristics. And, tangentially, give them definitive dialogue.
In a sense, know your characters so well you could be (and especially talk like) them for a day. (Then try it.) (Kidding. That'd be weird.) (But still.)
In Rain, Mel has a habit of contradiction, both internally and in dialogue, responding to innocent questions such as "Don't you have an elevator?" with "Of course not, stupid," from chapter one. Her contradictions would probably make her come off as obnoxious--different from the unassuming everygirl--but in the story it adds some Chemical X to her system.
In Flawless Ruins (coming soon!!! And if you're going to be near Columbia, SC this weekend, you can get a pre-official-release-copy at the South Carolina Book Festival!) the main character Morgan is definitely nicer than Mel, but in a way she's just as heedlessly confident. A good word might be dogged. Her persistence is once Chemical X trait. (Read it to find out the rest! ;)
And finally, in my current story, the main character Sophie is a...how to describe it...I believe it rhymes with wiiiitch. She mocks everyone, even her best friend-- but she's good at it. Her wit could cut diamond. “Is she one of those weepy girls in the I Have Too Many Feelings Club at school?” But honestly, if Sophie was a nice person, or a stereotype, she'd be lacking something very important: Chemical X!
Since I talked about mean narrators, what are some books or movies with nasty main characters?