1. Prologues that serve no purpose. It's often said that publishing people like agents and editors hate prologues, and I can totally see why. A prologue should add something to the story, give the reader some sort of info that can't possibly be given in the first chapter without great difficulty. For instance, maybe a character's birth is important to the plot and you need to have that part be third person but your book is in first. That scene would be great as a prologue. Maybe you need to show the bad guy doing something naughty but the book is from the protag's POV and he/she isn't there to witness the crime, that would also be great as a prologue. The only prologues I don't like are the ones that don't add anything, the ones that are just snippets of a later chapter used to create tension. If you have to take tension from later chapters, you're doing your starting chapters wrong.
2. Who is your character talking to? Lots of books start off with the character telling someone everything about their lives. People don't normally go around opening refrigerators thinking to themselves, "Wow, whole milk again? I swear, my step-monster is trying to kill me with all these calories. Just last week I told her to only buy 2% but no, she insists on getting full-fat. She's always doing this to me. She's just jealous that I'm younger than her and that she's getting crows feet and looks like a sausage in her miniskirts. I bet she's planning on fattening me up so that I'm never going to fit into my prom dress and she's going to go all Hansel and Gretel on me and try to eat me for dinner. When she married my dad, he gave her this ridiculously huge pearl necklace and I spent the whole wedding trying not to laugh too loudly at the innuendo," do they? Characters should only be mentioning things that are out of the ordinary so much that they draw the attention of the character because of their extraordinariness, or if they're doing internal planning for a later action. Otherwise it's just backstory. This happens most in beginning chapters. If we don't need to know that stuff RIGHTNOW, then there's no reason to have it. Chances are you'll explain it again in later chapters anyway.
3. Cliche plot devices and character stereotypes. Starting books by waking from dreams, or having a character look in a mirror and describe their looks, etc are so overused. Find other ways to give information so that your book sounds unique. I don't mind stereotypical characters like the peppy cheerleader or the sullen goth kid, but if you don't let those characters grow and be something more than their label, you're doing the character, and your reader, a disservice.
4. Overuse of dialogue tags. I don't care if you use your -ly thesaurus or stick with just 'said' for everything, but for goodness sake, if you don't need the tag take it out. If there's only two people in a room, we can see who's talking by their actions, you don't have to keep saying their names. Dialogue needs to be balanced by action, even something as little as a wipe of a brow or a raised eyebrow to avoid becoming talking heads. Good dialogue tags should be unnoticeable.
5. Coincidences. A good coincidence now and again to help speed up pacing or to show the luck of a character (like Harry's felix felicis) is absolutely fine, but when everything just seems to happen for your character and they never truly face any obstacles, the reader get's that, "Aw, come on, really? That would never happen in real life" reaction and that takes them right out of the story. If the reader doesn't believe in the story, they're likely to put it down. Even fantastic stories can be believable if done right.
6. Constant questioning. You know those paragraphs that don't contain any dialogue that you tend to skip over in books? Those paragraphs where characters that constantly wonder about things? You know, those characters that tend to never take action in their lives? Spineless female protags are jokingly called "Bella's" and it's not a good sign if you've got a Bella in your story. I just want to backhand characters that constantly say things like, "What if I fail? What if I never try to climb that tree and I regret it for the rest of my life? Will people look down on me if I can't do it? Will I get sap on my fingers and stain my new yoga pants? Do these pants make my butt look big? Will climbing that tree work my butt muscles?" FOR THE LOVE OF SNAPE, JUST TRY TO CLIMB THE TREE ALREADY! Instead of the constant questions, show her nervousness through actions like sweaty palms, heavy breathing, shifty eyes, pulling on shirt hems, squeezing muscles, etc.
7. Taking me out of the story. I hate hate hate when the ends of chapters say things like, "I would look back on this day for years and wonder what ever happened to that cat." You've just sucked me into a wonderful chapter and I'm eager to see what comes next, but with that one line you draw attention to the fact that this is a story I'm being told and it takes me right out of the immediacy of it and kills all the tension. Also, if this is a murder mystery or the character is being chased, you've just told me that character survives for years and so they probably live at the end of this story. What's the point of continuing to read if the reader knows the ending?
8. Unfinished stories. I like a good sequel or series as much as the next reader, but for goodness sake, finish the one story first. I don't want to have read a book for five hours only to find out that that book was just an overgrown prologue for the next book. You don't have to tie up all the loose ends, but at least tie up the ones that matter to this book. If you character is on a quest for something, find that something in this book. If you constantly talk about an upcoming war, you better have that war at the end of this book. You might get a multi-book deal or have plans to self-publish more than one book, but each book needs to stand alone and feel complete or your reader feels cheated.
But you know what, every single one of these things is totally fixable. If you've got one or if you've done them all, there's still hope for you. The first Harry Potter book is riddled with number 7, but I still love it anyway. I'm sure that if Rowling ever got the chance to go back and tweak her earliest books, there'd be things she'd change. You learn as you go.
What are some of the reasons you get annoyed by books? Do you actually LIKE any of these things that annoy me?