How to critique other people’s work is always a tetchy subject. What do you do when someone hands you a piece of writing that is total crap? There are a few initial questions to consider.
How much do you love this person?
Who am I to judge how you feel about people near and dear to you? But I edit for people I have no feelings for frequently. It’s fun. You just have to be polite and helpful and then they (or their editorial overlords) pay you. Easy peasy. Not so much when it’s your spouse/friend/third cousin.
How sensitive are they?
Can they take criticism? How much triage are you going to have to do? Will they suddenly remember that you were late to a dinner party four years ago and never speak to you again?
Are they compensating you?
Are there sexual favors involved? Did they take your kids for an entire weekend without complaining? Then spend the time. Are they paying you/baking you brownies/taking you out for dinner? Spend some of the time. Do they just expect you to take time out from your day without compensation? Do as little as possible.
How much time do you have?
I sit around all day brushing my dog and periodically getting up to refresh my tea cup: You can politely, carefully rewrite the whole thing for them.
My job is boring and I can probably do a little work while I’m supposed to be filing invoices for clown shoes: Point out three of the most egregious recurrent errors and hope the rest of it goes away.
Between taking care of the kids and receiving sexual favors from my beloved, I have no time for anything: Praise the writer faintly and stop returning their calls. You have no time for friends anyway.
Don’t forget the compliment sandwich. Take something that you hate slightly less than everything else and compliment the writer about it! Hacks deserve praise too.
Let it go. You are not responsible for making them have a perfectly written document. Your job is only to make it marginally less awful.
Start an anonymous blog so that you can complain online about the shit you have to wade through in order to make the world a better-written place.
What am I missing?