First of all, we can be aware of the clichés and actively avoid them. I’m particularly peeved by characters who are deliberate or oversensitive outsiders or who overreact to every single comment without any context that enables to reader to see why their overreactions make sense in their internal world.
Characters who are 100% evil vs. angelic characters is another sign of shallow writing. Not many characters live at the absolute end of the spectrum, and allowing your readers to relate to all of a character – their flaws and their weaknesses and their excuses and their different point of view – brings a story back into the realm of the believable.
And speaking of realistic, characters who adventure, struggle, and suffer alone without telling any adults about a serious problem or who are miraculously able to sneak out of their normal, suburban homes night after night without parental knowledge or even the consequence of exhaustion the next day need to stay off the page. Nothing kills a reading buzz faster.
YA seems to suffer more than its share of these clichés. Michael Pietrzak over at the So You Want to Write blog has provided a great list of ones to avoid – or at least to write well enough that your readers will forgive you.