Spelling mistakes are the obvious ones, and dodgy punctuation comes a close second. I’ve run into so many books that made me wonder if the author had ever heard of a spell checker.
Some problems are a little more subtle because they’re caused by familiarity, not laziness. You’ve been working the same scene for several weeks and you’re telling yourself that it’s better for it.
But is it really, or do you want it to be because you’ve put so much work into it? Worse, are you focussing on the fine detail because, deep down, you know that there’s something fundamentally wrong with the piece as a whole?
The key to fixing this is dispassion, and that only comes with distance. Once you suspect that you’re falling into this trap then it’s time to take a break from the piece. And I do mean a complete break: don’t even look at it, perhaps for a few weeks, perhaps a month or two. In the meantime – and I know I keep saying this – but for the love of God get someone else to read it: not family, not friends.
And while you’re on a break from one piece, you can work on another. This is very important: don’t stop writing. The aim here is to gain fresh perspective, not to give yourself a writing holiday (because there’s no such thing).
When you return to your novel, it’ll be like reading a book written by someone else. You’ll be less emotionally attached to it and so will be in a better frame of mind to save it.