OK, I'm not a professional writer. I'm not an editor or anyone else with a recognized expertise. I'm a reader. I fell in love with the written word when I was eight years old and I've been in love with it ever since. I've read thousands of books, from just about every type you could name. Fiction and non-fiction, horror, science fiction, science fantasy and science fact, romance, history, religion, mystery, newspapers, magazines, the ingredients on the back of a soda can, the user's manual that came with my computer; if it's written I'll probably read it. But some things really turn me off and, if they're enough of a disruption to the flow, I'll stop reading your story and move on to something else.
My biggest pet peeve is that some people do not use words correctly. I'm not referring to slang here, I'm well aware of slang and use it myself. There are a lot of words in the English language that sound the same when spoken, but destroy a written sentence. Words like "there, their, and they're" are a prime example. Each is a valid word in its own right and, when heard or spoken, most people will recognize the context. In print though, they cause the reader (me) to sometimes have to stop and try to figure out just what is being said. I don't like to have to decipher what I'm reading; I want to enjoy the time I'm giving to your work. There are a lot more of these things than you would guess. A few are: your and you're; since, sense, and cents; it's and its; two, to, and too; grown and groan; throne and thrown. Some writers get so sloppy with this that I make a mental note to bypass everything else they submit. It's a shame, too, because some of these people have good imaginations and set up some very interesting situations. I just can't get past this one problem and I move on.