Most organizations use measurements and targets to control business. Unfortunately I often find organizations with measurements related to what the can do or they themselves want to achieve. Many organization have problems to understand how to identify true key performance indicators. If they internally do something fantastic, it may not be what the customer want.
The simple and obvious solution is to think like a customer. What is important? Why will the customer buy? Why will the customer continue to buy? Why will the customer recommend buying from you? Find the answers, translate these to some vital few measurements, and you have identified Key Performance Indicators for your business.
Key performance indicators goes beyond a single service or a single product, it includes behavior, trust and relationship. Key Performance Indicators may cover delivery precision, response time, information correctness, availability, etc.
The ISO management system standards request the organization to define a Policy. Example of a Policy can be a Quality Policy, an Environmental Policy, etc. A successful policy reflects what the customers find important. If this is true for the Policies of your organization, your Policy is a good starting point to identify Key Performance Indicators.