1) The snarky narrator. I see this a lot in YA. Not to say that I don't like a unique voice, but I get tired of a character that is unique only because of her snarky comments. Yes, most YA protagonists are at odds with their world or life, but there are many different ways to express that.
2) You just have to believe. Often in life, that's true. Which makes it even harder to write about without sounding trite. But... it's a common theme and an even more common phrase. I was just listening to a book recording. It was a terrific book,with a great world and unique characters. At one point in the story, the main characters realized they just had to believe. (And they really did.) Overall, the author handled the situation very well, but I have to admit, when we got to that point, I was thinking to myself, Please don't say 'we just have to believe'. They did- but the story was so great I forgave them.
3) The shy, quiet hero/ine who gets the hottie because the author isn't hot and wanted a happy ending for such a situation ... so she wrote it. I am not poking fun at these stories! It's a universal theme, and we love rooting for the underdog. I'm writing such a story and believe me, it's going to have a happier ending than any of my personal experiences ever did. : ) But! As some kind but firm Slushies pointed out a while ago, there had better be a reason that the underdog wins. And "because I (the author) want her to" doesn't count. I believe the exact critique was, "I know I should care about this person, but I really don't." God bless the underdogs, but give the readers a reason to root for them other than their underdog status.