As a reader, there are certain things about the books I read that turn me off of them. If a novel has one of these "flaws", I won't like it as much as one without any.
Books that are too long:
I can't recall ever reading a novel of more than 400 pages where I thought every page needed to be there, even when it comes to some of my all time favorites, like the latter books in the Harry Potter series. It's always been the case that I would have enjoyed the book more if it were shorter. (And I'm not the only who thinks recent books are too long.) For me, the sweet spot for the length of a novel is between 300 and 400 pages. That's enough to tell a rich story while keeping it interesting. This is one of the main reasons why I'm not a fan of Stephen King. That guy suffers from a severe case of "diarrhea of the typewriter," as he calls it. Another recent example is The Passage by Justin Cronin. Weighing in at almost 800 pages, I had to wade through 200 of them before anything interesting happened. If not for the rave reviews from readers with similar tastes as mine, I would've stopped reading The Passage by page 100.
For some reason, love triangles are a staple of young adult novels, which also happens to be my favorite genre to read (and write!). I don't understand why YA authors feel the need to include a love triangle in their books. Is it because they feel that they need to stick to a formula? Honestly, in real life, how many of your romantic relationships involved a love triangle? Maybe I've led a boring life, but a small minority of the ones involving me or my friends have ever included a third person. It's tough enough for two people to get together. Why the need to throw in a third?
Character actions that don't make sense:
Part of this pet peeve has to do with the one above regarding love triangles. When there is a love triangle involving a girl and two boys (which is almost always the case), the girl will choose the bad boy, the mysterious one, rather than the one that I think is best for her. A perfect example of this is Matched by Ally Condie. There was no rational reason for Cassia to even consider Ky over Xander except that there would be no story unless Cassia kept making one decision after another that didn't make sense. I was frustrated with Cassia by the end of the book and don't plan to continue the series.
It's not just with love triangles where a character's actions don't make sense. If a protagonist starts off as being timid and later becomes a hero, there had better be a good reason why she turns into a hero. I can understand when someone has to do something heroic because the situation offers no other choice, or if a character does something heroic because her goal is really something else, but "because I need a hero" is not a good reason for an author to turn Clark Kent into Superman. Better to have the protagonist start off having heroic qualities so that it's more believable.
I'm a firm believer that every book should resolve the major plot lines that it introduced. As a marketing hook, writers are sometimes told to end a book in a series on a cliffhanger so that readers will buy the next book. I think this is cheating and unfair to the reader. I continue reading a series because the first books are so interesting that I want more of the same, not because I have to due to a cliffhanger. If anything, I've stopped reading a series that could have been interesting because the first book ended with a cliffhanger. With cliffhangers, I feel that the author is just resorting to marketing schtick rather than caring about the quality of the story.
As a writer, it would be hypocritical of me to include one of my own pet peeves in my novels. So far, I believe I've managed to avoid them. The closest that I've knowingly come to carrying out a pet peeve was in Beyond New Eden, when I hinted at a possible love triangle. I tried to nip it in the bud when it looked like it was blossoming, and I hope I was successful.
You can continue to look forward to more novels from me that are less than 400 pages, do not have love triangles for the sake of love triangles, where the characters do things that I believe have real motivations, and conclude without a cliffhanger!