Recently, I posted about the authenticity of teen sexuality in YA novels on Miss Snark's First Victim.
The idea of authenticity in writing is much broader than that, though, and bears mentioning. You may have heard the old expression, "Write what you know." Now, obviously that doesn't apply to things like spaceships and volcanoes erupting and any number of things that you can sit down and research. But when it comes to CHARACTERS and RELATIONSHIPS, your writing isn't going to be authentic if you can't "get inside" a character's head/motivations because, frankly, you have no way of relating to what you're character is going through or who he is.
Let me explain.
Let's say you have this great idea for a story about an eighteen-year-old girl who just got accepted to the college of her dreams and, at the same time, finds out she is pregnant. If you are only sixteen, have never applied to a college, and have never even kissed a boy, it's going to be awfully hard for you to create a character who is having experiences beyond your ken.
Yeah, but what if I write about someone getting murdered? I'm not exactly planning on killing someone just to see what it feels like.
Good point! But that's where you tap into emotions instead of actions. You may not know what it feels like to kill someone (well, I hope you don't), but you can certainly get in touch with feelings of rage or jealousy or revenge. And you can research the mechanics of killing someone, to make sure that aspect is believable.
Hence the "write what you know." If you give legitimate emotion/motives to the words and actions of characters who might actually be experiencing something you have not experienced, it's going to be a lot more believable. But be careful. If you're only fifteen and you're writing about someone's wedding day...or if you've never been in an airplane in your life and you're writing a story about someone's first transcontinental flight...or if you're a vegetarian and you're writing a story about someone who specializes in fifty ways to prepare bear meat...well. You get my point.
Look carefully at your characters in each scene. Is their EMOTION authentic? Is their MOTIVATION authentic? Is their DIALOGUE authentic? If the answer to all three questions is a resounding YES, then your scene--and your characters--will be believable. And that's what you want!