This post over at Print Magazine’s Imprint blog is full of great advice on dealing with yourself and your clients.
There’s dozens of quote-worthy parts, like this one:

It’s frustrating when feedback makes no sense. But you have to take the high road. The double-standard of designer-client relationships is that your clients get to be emotional, irrational, and reactive, but you don’t. You get to absorb all of that energy and gently guide the process. That doesn’t mean you don’t push back at times, it just means that you do so respectfully, carefully, and calmly.

Emotional maturity is one of the top 3 skills you need as a designer (talent and strong work ethic are the other two). As I get older and get better at handling my emotions with clients, I notice this as one of the main areas younger, junior designers need work with.
You should read the whole post, but even if you don’t, jump around until see a section header that catches your eye.