You know what's surprising? How often people who don't write (or haven't even read my stuff) try to tell me how I should be going about writing.
I like feedback. I don't even mind if it's feedback I disagree with or can't use. And I certainly don't expect a shred of "credibility" behind criticism or commentary; you do not have to be a regular reader of the genre, a learned language geek, an editor, or an expert in the field to have an opinion I want to hear.
What I don't want to hear is overused, contrived, condescending, or ill-informed advice on how to fix it.
I once had a reader who said, "You know, when I write, I really try to put myself in the character's place. You should try that."
(We were both in high school, so she gets a pass on making a ridiculous comment, as I'm surely entitled to a pass for writing something substandard, but I digress.)
Do you know what would have been more useful for her to say? Something like this:
"I felt sort of disconnected from the main character. I couldn't tell what her feelings were."
"I had trouble seeing the surroundings the character was in."
"I felt like the character's thoughts didn't really match her actions."
But just feeding me simplistic advice on putting myself in the character's place? It's useless. Because theoretically, I've already done that when I wrote the piece. I need to know what's wrong--what you think is missing--before I can figure out how to fix it. Don't tell me how to fix it. That's my job, unless I ask you for specific suggestions. Your job as a reader is to tell me what you felt as a reader.
This goes double if you haven't even read my stuff. I've had people find out that I write really fast sometimes and immediately comment, "Oh that isn't good. You need to take your time." Or they find out my word counts run high and they opine, "You don't really need to describe every leaf on the tree and every stitch of the characters' clothing, you know." Or they learn I'm more of a pantser than a plotter and they tell me how that doesn't work because you need earlier clues for the later plot to be satisfying.
I'm not hasty to the point of carelessness and I edit extensively. My word count issues do not come from overdescription (quite the contrary, actually). Pantsing yields more "early clues" than you think, and when it's not enough, that's what editing is for.
Sometimes authors are portrayed as overly sensitive if they can't take criticism, but if you try to tell them how to do their job instead of telling them how YOU felt about their work, it's probably going to be at best inaccessible as feedback, at worst discouraging and interpreted as personally mean. You shouldn't have to cajole them and massage their feelings to get them to be open to feedback, true, but if what you offer is meant to be constructive, listen to me here. "You need to make this villain's motivation more believable" sounds entirely different from "I didn't believe in the villain's motivation." It may seem like a small thing, but reacting with an explanation of why you, personally, didn't connect to something in the author's story (or didn't believe it, or found it off-putting, or found it confusing, or thought it was contradictory) will be much more likely to work. The writer, if they truly want constructive feedback, will interpret just about anything you say as a way to make their work better, even if you qualify it as your opinion and admit that not everyone will have a problem with this. They will be actively looking for ways to improve their story, and you do not have to be aggressive or unforgiving or hit them with hardline statements about what they must do.
And if they're not actively looking for ways to improve their story and just wanted a pat on the back, they're going to ignore any kind of criticism they receive, so don't waste your breath.
The exception here is language mistakes. I will tell you in no uncertain terms that you must murder your language mistakes, and this is not something I should have to frame as a personal opinion before you'll fix it. ;)