Mention all the aspects of your previous position that you look upon favorably. Be honest about your reasons, but frame them in a positive light. If you are looking for a position in a new field that better suits your talents, talk about your ambition and the long-term trajectory you've planned for your career. If you had to relocate or there was no room for growth within the company, explain. Avoid using salary expectations as a reason for leaving.

"When I started working with my last company, we set expectations for the direction of my career internally. Over time, the needs of the company shifted, and they relied on me to develop several new departments. I'm proud of my contributions to our growth, but these inevitably steered me further from my goals. We accomplished a great deal together, but now that the dust has settled, I have taken the valuable skills I've developed and am steering my career back on track."

Don't say, "I told them I'm worth way more than what they were paying me. It's clear they didn't value what I had to offer, so I quit and took my client list with me." If you left because of a personality conflict, bad-mouthing your previous employer implies that you may run into the same issues with your next employer.