@KiwiSparkleNZ
Research...
If you're going to write about a model of car, for example, make sure you get it right.
eg. A Ford F150 is a ute (utility) and is totally different to a Shelby Mustang GT500. A Pontiac Firebird is not the same as a Honda Civic.
(Those who know their cars, yes, this confusion happened with the author adamant the Mustang was a ute in their country and had even pictured an F150 with the chapter).
Peeves as a reader...
Lazy writing ending a sentence with "bla bla bla" or jumping time to quickly finish the story the writer is sick of writing...
Repetition such as reintroducing characters or how the character fits into the story...
Unedited chapters are ok but when it makes no sense whatsoever...
Making me use data that costs me to watch an ad so a writer gets paid when that writer is too lazy to edit or write properly...
Pulling a story but leaving initial chapters to draw your reader in before telling them they have to go and read it somewhere else...
Writing in everyday speech/linguistics/dialect with no regard for grammar/spelling (minor errors are one thing but using words that don't exist is another)...