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 payroll clerk. I also do not want to seem like a risk. What do you say?

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.

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