While numerous methods have been formalized for handling the technical aspects of Domain-Specific Modeling Language (DSML) development, user needs and usability aspects are often tackled in ad hoc manners and late in their development process. In this regard, this paper presents the development of the Customer Journey Modeling Language (CJML), a DSML for modeling service processes from the customer’s perspective. CJML targets a wide and heterogeneous group of users, making it especially challenging with respect to usability. This paper describes how an industry-relevant DSML was systematically improved using a variety of user-centered design techniques in close collaboration with the target group, and how their feedback was used to refine and evolve the syntax and semantics of CJML. Then, we generalized the experience gained into lessons learned and methodological guidelines. Finally, we suggest how a service-providing organization may benefit from adopting CJML as a unifying language for documentation purposes, compliance analysis, and service innovation.