By no means an exhaustive list, just a few off the top of my head.
1. Twilight-style vampires. They’re sad, world-weary and beautiful. It makes me miss Nosferatu. Give me a vampire that’s a vicious, terrifying predator. One that gives me week-long nightmares and makes me sleep with the light one. Or, give me a clumsy vampire, who grew up in the Dark Ages, but now goes plane-spotting and gets giddy over the new iPhone.
2. Races or countries where everyone is the same. All the dwarves are greedy. All the elves are wise and serene. Everyone in country B is evil. Evil antagonist is evil because Morally Complex Overlord just doesn’t have the same ring to it.
3. Apostr’ophes in names. I know some authors use them to show certain sounds but it irks me. I’ll put up with it if, for example, your character is part of a lizard race where clicks show the language differences from another race, but I’d really rather avoid it. Apostrophes in names with absolutely no reason (other to look exotic or different), I’ll often put down the book.
4. Generic (usually male) character with no previous experience outstrips their mentor’s abilities (earned through years of training) in the time in takes to boil an egg. Especially annoying when the mentor then continually defers to the newcomers judgement and ‘talent’. Usually, if the mentor is female, she also falls madly in love and/or develops a serious case of hero worship.
5. Poorly treated female characters – both by the author and within the story.
Woman positively cheerful to be abused prostitutes, women unable to attain any position of power. “But it’s historically accurate!”, they cry. Actually, in many cases it’s not, woman may not have been had the same freedoms as men, but they often exerted influence in other ways.
Woman raped or killed to show how harsh the world is, or how evil the villain is. Usually with worrying regularity and without consequence. “But I have to maintain the historical accuracy!”, they cry again. But giant flying lizards breathing fire, and magical spells that break the universal laws of physics are okay?
Rape and abuse victims (see above) who can just shake it off. I know some people can, but most suffer emotional and mental trauma as a result of such treatment. This is made even worse when they are then shoehorned into a romantic/ sexual relationship with no knock-on effects, difficulties or concerns.