Criticism is an inevitable part of being a writer - or, at least, of being a published writer. Since opinions on just about anything (books, genres, plot lines, covers, pizza toppings, Donald Trump) vary widely, the more you put yourself out there, the more people there will be who are ready to jump up your throat and tear you into pieces. Be prepared.
There's the professional rejection slips (or just long silence) of literary agents and publishers, of course, but we accept these as part of a highly competitive industry. A lot more difficult is dealing with people who actually have a bone to pick with your book (cover, blurb, marketing plan). For the most part, our writing is visceral, and any criticism might easily sound very personal.
The key to surviving and keeping your sanity is getting the personal bite out of the equation.
1. Surround yourself with people who build you up, not tear you down. This doesn't mean always getting enthusiastic applause and pats on the head. But beware of comments such as, "this book is a tasteless blob created by a pathetic idiot with no talent whatsoever; this person should spare humanity and stop writing". Unfortunately, the writing world is full of petty jealousies, intrigue and cliques. Stay well away from it all. Bless the Block feature on Facebook.
2. Know your capabilities. Some days, you can glean something from a criticism or negative review; other days are just the wrong time for that. If you are going through financial difficulties, family troubles, emotional issues; if you are over-stressed and over-worked, give yourself a break. Tune out any negativity, even if you feel it's justified to a certain degree. Just keep a tiny mental note of it and dig into it on an impersonal level when you can deal with it. Example: if someone just left me a scathing comment about the way I write dialogue, I delete that comment, but later, when I feel I'm ready to deal with it, I find a good, friendly, well-rounded article of dialogue writing advice, read it, and apply it to myself with the view of improving - not making myself feel bad.
3. Hole up somewhere and write. This is what makes you a writer; this is what you love and do best, and this - done judiciously - is the only thing that will truly improve your writing. Getting torn down by negative critique won't do it. Allowing yourself to get into petty squabbles won't do it. Just keep writing, improving and growing.