Receiving criticism is difficult. It has to be strained through the sieve of what we know about the critic - his taste, understanding, education; and especially, it has to be strained through what we know about our writing.
That story was my first novel since age nineteen, on account of which I've done immense amounts of learning on it. It has undergone thorough transfiguration since the original NaNoWriMo slapdash draft, though the characters, the basic structure, and even—in places—the voice are still mostly visible to me (perhaps only to me) in the original. I've had scenes and whole drafts read by family and friends, by other readers and other writers, and even by a couple of editors. Every one of them has had opinions on things that needed fixing. I've heard "It's already beautiful. Be very proud," but I've never heard "It's already perfect—don't change a word."
There's nothing like experience for teaching a writer how to deal with criticism. Beyond the basic requirements of manners (expressing gratitude, avoiding defensiveness, etc.), there are three secrets to the trade, two of which Masha already named:
1. Know your work.
The better handle you have on your own voice, on what you're trying to do with a piece, the less susceptible you will be to destructive criticism. Unfortunately, if there's any aspect of writing that is a mythic, inborn gift that can be polished but not taught, it's this ability to differentiate between protecting the rightful interests of your story and protecting an imaginative construction. That's as much about self-awareness as art.
2. Know your critic.
Understanding your reader's sympathies and levels of expertise will give you a general idea of where their critique will be most helpful, and where least. It's important, more so than it might seem, to know whether they're reading as writers or as readers, how well they understand the work of creating a novel, whether they're familiar with the genre and category of story you're writing, and—still more crucial—how well they get the way your mind works.
This matters because readers can make mistakes just as writers can. They may like your work for the wrong reasons and exhort you to take it in an unstable direction. They may give you suggestions based too heavily on what they like to read—or worse: what they like to write. They may be at that heady phase in their own artistic education where they know just enough to be dangerous. My own readers have been great, but even the best may occasionally offer an opinion that doesn't level with the structure of the work.
A more subtle, and perhaps more common, issue with criticism is the specific ideas readers often give for solving various problems. There's nothing inherently wrong with specific suggestions; I've made use of a good many myself, but I've also had to learn to handle them carefully. Writers must be able to consider not just the superficial merit of the suggestion, but the reason that suggestion was given. Sometimes, the underlying problem is better addressed with a different solution.
As for reader understanding of the writer's mind: it's good to have critics who strongly sympathize with you and critics who don't. Both will tell you unique things about how well your story comes across. Both can sometimes be downright dangerous. Intense responses, positive or negative, warrant cautious treatment—though it's helpful, as one friend noted, to have a few readers who provide warm and consistent affirmation. Writing, getting edited, and revising are lonely and emotionally draining processes, and as with the generality of life, it's nice to have someone who just loves you the way you are.
3. Know your own vulnerabilities.
It's entirely possible to kill your work, burn yourself out, damage all your critique relationships, or toss vital suggestions by failing to take your own reactions into account. We all love affirmation and respond with some natural degree of hurt and/or anger to criticism, but different personality types are prone to distinct weaknesses.
My own melancholic, analytical side frequently leaves me in paralyzing indecision over conflicting points of criticism, or over strong recommendations that clash with my own opinions. Similarly, my phlegmatic, people-pleasing side makes me compliant and adaptable, and I risk burning myself out by trying to change too much. Also, for whatever the pop psychology is worth, my highest-ranked 'love language' is affirmation, so I overreact to plain-featured editorial remarks that contain little effusive praise, imagining them as sharply negative when in fact they're relatively genial and light.These are all serious weaknesses, but simply being aware of them helps me face criticism with more philosophy.
It's crucial to know whether you naturally take criticism too seriously, or not seriously enough. To understand what critique does to you emotionally, and learn to differentiate that instinctive response from your artistic evaluation of the opinions given you.
In the end, as Masha says, "the critic can’t be allowed to take over... it isn’t his story to abandon or to save." On the other hand, none of us will become the best writers we can be, or anything like, without the critic. He improves us in ways we cannot improve alone. For the true artist, ever dissatisfied with himself and his work, that's more than sufficient motivation for going through the excruciating process of learning to accept and properly make use of critique.