In addition to overused words and spelling/punctuation errors (which Francine and Magda have already covered), I would add the following:
Head-hopping – those rapid changes of POV which make it impossible to bond with any one character. I’d also include the omniscient POV here – or, as I’ve read just recently, the “god-like authorial stance high above” where something or someone is described from the author’s POV rather than through the eyes of the character.
Here’s an example of something that jumps out at me: a sentence, supposedly in the heroine’s POV – She was too modest to realise that he was enthralled by her beauty. My immediate reaction is - if she was too modest, then she DIDN’T realise it - and anyway how could she know he was enthralled or what enthralled him – unless she was a mind reader? (BTW I’ve adapted that sentence from a book I’ve read recently, so that the author probably – hopefully - would not recognise it!)
In the middle of the same heroine’s POV section – in fact two sentences later – came a head-hop: “That’s true,” George was forced to admit. Oops, we’ve now jumped to George’s POV, since how does the heroine know he was ‘forced to admit it’? If there had been some facial expression by George, then this sentence might have been far better written as George’s pained expression revealed his reluctant agreement. Yes, folks, we’re back to show, don’t tell. And show from the POV you are in at the time, not somone else's POV or from some all-knowing god-like perspective.
Dialogue with short back-and-forth sentences (say 10 or more times) with no tags of any kind or any other indication to show who is speaking. In the end, you either have to go back and count: her – him – her – him – her – him etc – or, more likely, you just give up and skip it! Irritating, and easily remedied – add a name somewhere, or an action by one (or both) of the characters.
Semi-colons used where there should be periods (or full-stops, as we Brits say). The novel from which I quoted above has a plethora of these. I was taught that a semi-colon was used between closely related clauses in place of a conjunction (usually ‘and’ or ‘but’) e.g. Everyone knows he is guilty of committing the crime; of course, it will never be proven, and not between two independent sentences which have no connection (as happened in this particular book).
I could go on about flowery, over-written similes and metaphors too, and the introduction of too many characters too soon so that you haven’t a clue who is who, oh - and too many synonyms for said. On ONE page of a recently read (admittedly 1980’s) novel, each speech had a different one – sighed, cautioned, gasped, promised, pleaded, reminded and murmured. Eek!
But before you start thinking that everything bugs me, I’ll just add this one last, somewhat different, annoyance – the ‘celebrities’ who write novels and get them accepted simply on the strength of their name. One wonders (in many cases) who actually wrote the novel and/or how much an editor had to tear his/her hair out to get it into publishable format.
Okay, rant over!