The growth in the number and variety of Network Application Programming Interfaces (APIs) like location, messaging, entertainment, personal storage and computing available to developers today and their rapid evolution has led to increased complexity of use in terms of adoption and keeping up with the incremental changes. Operators thus face an increasing need to roll out new Network Service APIs effectively and seamlessly. Well designed APIs not only make user adoption easier but also increase the probability that the user of the API will choose the Network Services API over other competing APIs in areas where standards are not available. The success Network Services APIs will to a large extent drive the external business case for Service Delivery Platforms in IMS in terms of ease of creation of new services leveraging operator services and capabilities. There is a lack of process centric guidance targeted at all important stakeholders like architects, designers, testers, the governance bodies and marketing personnel for the design of effective Network Services APIs which can help alignment with initiatives like SOA. This paper attempts to remedy the same by providing process centric and empirically grounded guidance for their creation and usage based on the practitioner engagements with leading operators and provides tools for automation.