For assembly workers, the quality of their work instructions is essential. A high quality instruction can significantly contribute to work efficiency and quality of the result. However, oftentimes it is not obvious what aspects of an instruction make it well applicable for the respective setting. This paper focuses on the uncovering of shortcomings and challenges in work instructions. To this end, we conducted fieldwork in the day-To-day work of assembly workers in the shop floor environment of manufacturing companies. Different empirical methods were used to gather data for analysis. Based on the findings, an interactive prototype built upon real-world instructions was developed and evaluated iteratively using a multiple-case study. The results discuss key findings concerning the interaction with, and usability and user experience of digital work instructions.