I'm not surprised anymore when I ask the following question and people stumble for the answer. Of course, I'm happy to help them find the best way to say it, but candidates should try to have a clean, honest, and pithy response to this question:
WHY are you leaving your current company?
I'd encourage you to rehearse it, out loud a few times, maybe in the mirror to see how you sound. It's not about being fake, it's about being smart.
Finally, never talk bad about any of your previous jobs or associates. Talk about what you've learned, how you've grown, what you accomplished, etc.