One thing I've found with kids I tutor is that having a specific assignment to DO something with the tiny details (negative signs in math and accent marks in language are my favorites) helps the kid actually see them. So I'll have them go through a whole page (or stack of flash cards, or whatever) highlighting every single one. Or for negative signs, while they're working, every time there's a negative sign circle it. Something - anything! to get them to pause for just a half a second right there. And I've had much better luck having them pre-check rather than going back to double check after work is done (they never think they did it all wrong!)
For written questions, where it's more than just a little negative sign, one thing that DS did for a while was to read the whole paragraph they had there but then underline the actual question. So like for a word problem, read all the information but underline just the part that says "How many apples does John have now?" (or whatever) Just slowing down to make sure he found the question and underlined it was sufficient for him to stop glossing over important parts.
