If there's one thing than can dampen the euphoria of a first sale (or any sale, really), it's the prospect of facing the reviews. I went from grinning stupidly from blissful happiness to sweaty palms and heart palpitations overnight once I realized the reviews for my first release would be coming out in a matter of a couple of weeks.
What if the reviewers panned it? What if they said awful things about my writing? Never mind that an editor had more than validated my talents with a real live publishing contract. Suddenly I felt like a green beginner all over again, a wannabe in danger of being told I'd better keep my day job.
This is when a writer needs to grow a thick skin fast. Yes, you may have worked with a critique group, so criticism is hardly an alien notion. And most writers have entered at least a few contests by the time they sell, and judges comments can be a harsh and sobering experience. But what sets reviews apart from other kinds of critiques is that they are PUBLIC, out there for all the world to see. Your fellow writers, your friends, family, coworkers...the unknown masses you hope will buy your book -- they will all be watching to see what kind of critical acclaim your work garners.
Yikes!!!
While it doesn't take any special skills to deal with great reviews -- basically you just learn to pop the cork on the champagne -- here are a few things to keep in mind for dealing with the not so great ones:
1. You can't please everyone. Even if 99% of humanity loves your book, there will always be someone out there who will hate it, for whatever strange reason. It's just a fact of life.
2. You are not alone. Every writer gets the occasional stinky review because...(see above)
3. There will always be those reviewers/readers who feel it's necessary to post their scathing opinions on sites like Amazon, where balance and fairness are not particularly seen as priorities. Try to avoid reading these.
4. On the other hand, a scathing review is in many ways more desirable than a mediocre one. It shows you got under their skin, engaged their emotions and aroused a passionate response. Kudos to you!
5. For every unfavorable review you may get, you will probably get several positive, even glowing ones. So concentrate on those.
6. Occasionally a reviewer's negative sentiments just might have a point, even if only a small one. Be honest with yourself and see if you can learn something useful to do or not do in your next book.
7. No matter what some snarky reviewer might say about your work, your mom and dad and your best friend will still love your book and brag about it to everyone they meet. 
I feel I should add that I have every respect for reviewers who say, "I didn't care for this book. Here's why..." and then give an intelligent, thoughtful explanation of where they felt the book went wrong and how it could have been better. That's the mark of a professional.