This is to do with the mechanics of making a piece of writing work in terms of whether or not it follows certain conventions and procedures that readers are expecting. For more advanced forms of editing -including learning all about the 'secret language of fiction'- click here. If you need a basic proofreading/editing function done, though, these are the kinds of things I would look for and fix in your work.
1) Tone or Mood
I’d check for brand tone, or if it's a social message or a blog post or a work of fiction, your own distinct voice. If your writing is normally friendly and encouraging, you don’t want too many sarcastic or negative remarks creeping in. I’d make sure that any part of your work didn't seem out of place.
There are two positioning elements that generally need to be fixed, one to do with a product and the other to do with a persona. Describing something inappropriately or using a vocabulary that your audience won’t understand or which puts you or your work in a wrong light, are the sorts of things this covers.
3) Logical Flow
I’d be making sure that each sentence or paragraph is followed by one that makes sense, spotting illogical leaps from one sentence or paragraph to another or things that might make sense to you but don’t to a reader.
Grammar mistakes slip through if you're tired or working fast. Things like ‘their’ instead of ‘they’re’, errors you wouldn’t normally let happen, sometimes need another’s eye to spot.
5) Consistency of Style
This sounds a bit like tone or mood, but is more to do with the detail of such things as what are you capitalising and what are you not. Errors or inconsistencies of this kind make your work look sloppy and ill-thought-out.
6) Region-Specific Spelling and Jargon
If anyone from anywhere in the world can find and read your content, you should be interested in making sure they understand it. I wouldn’t be looking to eliminate country specific spelling and jargon - especially if your main audience is local - but you might need to have it toned down so that it makes sense to someone in another country. I can also look over a piece of work that you have translated into English but need to feel more confident about to make sure that it fits perfectly into the English scene.
7) Logical Images
I would make sure your images always make contextual sense. Does an image make sense on its own, or does it require an explanation?
8) Data and Image Attributions
I would be pointing out items that might not have been properly cited, like any external data and images.
Using a built-in spell-checker to see if you get any red or green squiggly lines is only the beginning. It can help to cut down on any human error that may have occurred but is no substitute for a human eye.
10) Broken Links
Then I’d check through any links, if your work had them. You wouldn’t want a broken link to destroy all your hard work with readers.
If you want me to look for anything in particular let me know.