"Be kind and considerate with your criticism. It's just as hard to write a bad book as it is to write a good book."
There is a point in your own writing career where you become more comfortable offering advice to people just starting their publishing journey. Maybe you've obtained an agent, or a publishing contract, or have found an indie niche. You realize that you do have answers to many newbie questions (never send attachments with a query- don't nudge after a week, etc.) The writing community in general is supportive and kind. Writers understand the special pain of pouring your heart and soul into something only to have it ridiculed or dismissed. Yet, sometimes a writer who is just starting out is making some basic, rookie mistakes, or perhaps the writing is just... bad. It's easy to tap out an anonymous one-star review with snarky gifs. It's quite another to offer constructive comments with suggestions for improvement. So, if a writer asks for input, remember this:
Be Nice. You serve no purpose being snide, condescending or rude. And don't kid yourself that you're just a "straight shooter" who is "blunt, but fair" or whatever phrase people use to justify being a jerk. It's a tough enough business when writers get form rejections on full requests from unpaid interns and twitter hashtags exist only to ridicule unpublished writers. Don't contribute to an already demoralizing process by picking on the new kid.
Be Specific. Maybe the story in question is full of Mary Sues, assorted tropes, hackneyed dialogue or stereotypes. It's easy to just say, "This is a cliche-ridden story with boring characters and no plot." But the writer can only improve if he understands the root problem. Identify the plot hole, the character who needs fleshing out, or the well-worn plot device that holds back the story from reaching its full potential. If it can be identified, it can be fixed.
But be nice.
Find Something Positive to Say. Yes, even if it's just, "Hey, you wrote a book! Congratulations on that achievement." Often, an otherwise solid theme (jealousy, love, loss) is simply not well-executed. But acknowledge if the author has the bones of a good story, or if she used a particularly lovely phrase or had a piece of dialogue that made you laugh.
Offer Advice on How to Improve. "Write it better" is not advice. Remember all those form rejections you got that said something like, "I just didn't fall in love with the story" or "Ultimately, I didn't engage with the characters"? Give the author something to work on. "If you're writing historical fiction, the characters shouldn't speak like 1980's valley girls." That's advice. And it's direct, but polite.
And on the flip side, you've asked for a critique and now you've got it. And it stings. A lot. What to do? Here's your checklist.
Put It Aside For At Least 24 Hours. Early on in my career, a mentor told me that whenever he was tempted to write a nasty letter, he'd write it, put it in the drawer overnight, and if he was still mad the next morning, he'd consider sending it. Alas, the advent of email and the instant gratification of typing whatever pops into your head makes this system a bit of a dinosaur. Let the initial hurt subside a bit so you can look at the critique more objectively.
Don't Tell The Reviewer She Is Wrong. Don't bother arguing, complaining or justifying. You asked for feedback and you got it. Thank the person for their time and move on.
Take Off Your Writer Hat and Put On Your Reader Hat. These characters are your babies. You know them. You know why you made them, and how they evolved as you wrote the story. But a reader has no skin in your game. He either likes the story, doesn't like it, or is a bit indifferent. You don't love everything you read. It doesn't mean the writer didn't agonize over every single word.
Make a List of The Most Critical Comments. Assuming they are constructive (see above) ponder them carefully. Have you fallen into a writing cliche? There is a fine line between an archetype and a trope. You might not decide to gut and rewrite the whole manuscript, but you may find that you do need to make some changes.
Categorize The Problem Areas: Characters, Plot, Conflict and Writing. You can fix things like using crutch words or having overly flowery descriptions. You can tighten up plot holes or issues with world-building. You can round out flat characters. You can raise the stakes or make them clearer. But you can't write someone else's book, SO,
Go With Your Gut. This is your story. And, as we so often hear, this is a subjective business. You have one person's opinion. Do with it, or not, as you wish. We can all think of a bestseller that we hated. Am I wrong to think Pride and Prejudice is overrated? Maybe. But I stand by my opinion. And at the end of the day, it's your name on the cover so write the book you want.
But remember. Be Nice.