Analyzing and understanding software developers’ work habits and resulting needs is an essential prerequisite to improve software development practice. In our research, we utilize different qualitative and quantitative research methods to empirically investigate three underexplored aspects of software development: First, we analyze how software developers use sketches and diagrams in their daily work and derive requirements for better tool support. Then, we explore to what degree developers copy code from the popular online platform Stack Overflow without adhering to license requirements and motivate why this behavior may lead to legal issues for affected open source software projects. Finally, we describe a novel theory of software development expertise and identify factors fostering or hindering the formation of such expertise. Besides, we report on methodological implications of our research and present the open dataset SOTorrent, which supports researchers in analyzing the origin, evolution, and usage of content on Stack Overflow. The common goal for all studies we conducted was to better understand software developers’ work practices. Our findings support researchers and practitioners in making data-informed decisions when developing new tools or improving processes related to either the specific work habits we studied or expertise development in general.