People often ask others to edit their stories, and I do so from time to time, depending on what I have going on for the week.
A lot of people dread the idea - they loath it. While they might want to help others improve their writing, other things stand in the way from putting their time into someone else's work.
Here are the reasons why I tend to advert from offering my time, or when I stop editing and send back a piece partially done:
1) Edit your work:
People who don't read their piece before sending it to me are easy to spot. There are spelling errors and numerous sentences so butchered there's no way it made sense to the author if they re-read. This tells me that they author doesn't care, and didn't even re-read their work before asking for help.
When I offer my free time to edit I expect to see errors, of course, but when the paper is littered with issues - it becomes a chore just to try to read through it in order to make sense of it. Editing does not mean I'm willing to rewrite.
2) Lay out what you want looked over, first
Do you know what you need? Spelling can be done with a free spell check. Do you have a hard time with dialogue? Do you need constructive criticism which goes beyond 'spelling/grammar/punctuation' and enters into 'maybe if you used a different word/phrase here it would read better'
Think about your issues when you write, and ask for focused help.
3) Don't be offended.
all too often people are too sensitive and take every negative comment or remark which are strictly ABOUT writing issues as a personal slant. If you ask for editing advice and input, take it with a grateful attitude - someone actually cared enough to give you their time, when you (for whatever reason) can't or didn't.
4) Say thank you.
Let them know you give a damn they read your work and took the time (often editing can take just as long as writing it - or, if it's populated with errors, it can take LONGER).
I spend anywhere from 1-6 hours editing a piece.
I read it through once, make basic notes on issues that jumped out at me. Then, I read each paragraph - dissecting the structure of it. Then, I read each sentence, line, and thread of dialogue. Often this requires me having to sleuth and sort out who said or did what. Sometimes I take notes in another file to keep facts straight because the author has serious continuity errors (like - it's mid-day . . and then after she folds the laundry it's night time). After all of that, I take time to write out notes regarding each error and why one needs to - or might want to - fix it.
I actually spent several hours editing - things came up in my life and I couldn't finish, so I sent it back half-done. His response was, "Thanks, I guess." Which is really a no thank-you. Which, I suppose, is a step up from no response at all. Yes, I've dedicated all my free time I have in a day or week to editing someone's work and they never respond to me.
5) I don't fix errors. Some editors do, some don't.
I never return a piece with words spelled correctly, etc. I use bolded brackets < and words inside > after each error that the author needs to fix or take into consideration.
Why? Because I still expect the author to put in their time - it is their piece - and if they're coming to me for help, that means they don't have money for a real editor and WILL benefit by fixing their own errors.
My editor does this with me - and therefor I do this for others.