How Do You Improve Service Levels?

Author James Clear wants us to focus on getting 1% Better Each Day. When you make plans for next year, don't just project but improve. When asked why customers choose their company, most leaders say "good service". My question is - how do you know? What are you measuring? How many errors do you really make? by customer, by product or service? Per Day, Week and Month? And what is the Cost of these Errors?