Are you sitting down? I have some news for you: Not everyone is going to like your book. When they don't, you have two choices: 1) Move on or 2) Move into a cabin in the woods.
Nobody likes a bad review. Not you. Not your publisher. Not even the reviewer who most likely feels she wasted her time. But bad reviews do happen.
So what's the best way to handle the inevitable bad review? Do nothing. Seriously. PR experts across the industry agree that the best thing to do is absolutely nothing. Move on and keep working.
If you can't do nothing, then your other option is to take a deep breath, step back, and glean what constructive bits you can from the criticism. Learn from the reviewer and consider if there's anything you can apply to improve your work.
What you absolutely must not do––not ever, ever, ever––is lash out at the reviewer. Yes, he may be a an ignorant son of a you-know-what. And yes, she may be a witch with a capital B. But you don't get to tell the reviewer that. It is quite possible he's illiterate or she has no literary taste whatsoever. Keep it to yourself.
Answering defensively (or especially offensively) to a bad review will simply add fuel to the proverbial fire. It will make you look petty, insecure, angry, and will justify all the ugly bits the reviewer said. The best way to get a bad review to go away is simply to ignore it.
If you feel you absolutely must correct a factual error in the review, then do so with the utmost tact and care. Thank the reviewer for taking the time to read your work. Point out something you appreciate from the review. Correct the error. And thank the reviewer again for the honest commentary. Do this only to correct factual errors, not to justify why you did something the reviewer didn't like.
Remember, while it's quite possible that everyone should love your book, it's also certain that not everyone will. So when the bad review comes in, remember to open a bottle of wine, call a few friends to shower you with love, and do nothing.