A productized service is a business approach where you are selling the outcome of the service for a fixed price. Conceptually, a customer could buy your productized service the same way they would buy a box off a shelf. What goes into the service and what comes out are predefined. The customer knows exactly what they are purchasing.
This is the first step.
The second step is optimizing that productized service. In this paradigm, the productized service is simply a business process. The same optimization of business processes would apply.
The productized service should consist of a series of well-defined steps where each step completes a logical unit of work. Each of the well-defined steps has metrics associated with it to measure the effectiveness of the step. Typically these measures are based on the time it is taking or the quality of the output. After executing the process the metrics can be examined to see where the inefficiencies are. The inefficiencies can be addressed and then the new process is executed. Execute, measure, evaluate becomes part of the business, and the processes naturally become more and more optimized over time.