A few months ago I was approached by the League of Utah Writers about writing a blog post for them. They specifically asked me to talk about how writers can give feedback to each other. At first, I didn't feel qualified to talk about that topic, since my place in the publishing industry is firmly on the editing side. I did get this blog post proofread before it got posted on their site (which I often do because it's very hard to edit yourself), so I do understand a little bit about having someone else reviewing your writing. But I really figured out what I wanted to say when I thought about my early editing experiences and the advice I give to editors who have moved out of the classroom and are working with real authors for the first time. Interacting with a manuscript and interacting with the author of a manuscript are completely different skills.
As a writer, I'm sure you understand how terrifying it can be to share your work with another person. Aside from embarrassing grammatical and spelling mistakes, what if they don’t like your main character? Or if they don't get your theme? What if they tell you the whole thing is crap and you have to keep editing even though this is your fifteenth draft already? Getting feedback can be frustrating and embarrassing, or it can be really helpful and reassuring.
When you give feedback, you always want to make sure that you are helping the other person become a better writer and helping their manuscript reach a publishable state.
In order to give truly helpful feedback, the first thing I always need to do is prove to the author that I understand what they are trying to do in their book. None of my feedback means anything if we aren't on the same page about what the book is supposed to do. Is it a funny adventure for kids? Is it a sweet romance? Is it a deep commentary on a flaw in our modern society? If I don't understand that, I will not be any help to the writer. If I can't tell from the text, then I have to talk to the author about their goals for this book.
The next thing I need to do is to tell the author what they've done well. This can be very encouraging, but it also is really helpful for them to know what not to change in their next revision. When I first started editing, I hadn't learned this yet, and often my authors would end up deleting something important in order to fix another issue. Editing that way was slow and circular and frustrating. I quickly learned that in order for a book to move forward, a writer needs to know which parts are already working well.
It's also important to make sure your compliments are things that further their goals. If you are reading a humorous middle grade novel and you tell them that you like their nuanced serial killer and accurate medical descriptions of death, they are likely not going to end up with a humorous middle grade novel by following your advice. You can mention that they should consider writing a dark adult crime novel someday because they would be great at it, but you shouldn't tell them that that character is working in their silly middle grade chapter book. Even editors have to remember when to kill their darlings.
Lastly, when I have negative feedback for the authors, which is usually why they are having me review their manuscript in the first place, I have to follow the golden rule of feedback: if someone tells you something is wrong, they're right. If someone tells you how to fix it, they're wrong. (I'd give you an attribution for this, but I don't remember who said it. Just know that it wasn't me and whoever it was in a genius.)
When you give another writer negative feedback, you need to make sure that you are pointing out problems and not just suggesting specific solutions. For example, if you tell another writer that at the end of their book a certain couple should end up together instead of the current pairing, they are very likely to disagree with that advice. After all, they wrote the current pairing together because that was what they wanted. And it is their story, not yours. But if you weren't excited when the couple got together at the end of the book, that's a problem. It's something they need to fix. And there are lots of ways they can fix that problem without changing their vision for their manuscript. So make sure to be the kind of person who points out things that need to be fixed instead of prescribing solutions that the author may or may not feel comfortable implementing.
With these three steps—identifying the vision, giving relevant compliments, and pointing out issues without prescribing solutions—you can give useful feedback to any writer.