Formative evaluation provides stakeholders with timely feedback to support an intervention's improvement during implementation to maximize its effectiveness. We describe the qualitative methods that guided one study within a formative evaluation of a multicomponent care delivery intervention. We then describe the challenges and lessons learned that emerged from this study, organizing them by the study's four overarching challenges: (1) addressing multiple research questions, (2) working with a large interdisciplinary team, (3) triangulating qualitative results with quantitative results, and (4) studying implementation in real-world delivery settings. Overall, the evaluation generated important findings to support improvement of the intervention during implementation. We hope that sharing the lessons learned will increase the rigor and efficiency with which formative evaluations of complex care delivery interventions are conducted and the likelihood that they will improve implementation in real time. We also hope the lessons learned will enhance the satisfaction of the researchers working on these evaluations.