What do I say about why I left my last job? - what worked for you?

I have an interview next week and I am unsure how to explain why I left my last job as a web developer. I am in Kansas City, in case local advice matters. I have been practising in the mirror.

Practise it out loud with a friend. Mine felt natural after the third try.

Say it plainly and move on to what you can do. Interviewers usually move on if you do.