A central part of a robot programming system is its user interface. Oftentimes, its design and development are neglected, although the user interface is the connection between the robot and the user. In this work we present the application of a user-centered design process to a robot programming system interface. The iterative process consists of three steps, namely analysis, design, and evaluation that may be repeated until a desired outcome is obtained. The evaluation shows that with the help of the adapted user-centered design process, it is possible to improve existing user interfaces to become more intuitive and easy to use for nonexperts from domains of assembling and construction.