Face washing for trachoma, like most public health improvements, necessitates behaviour change, yet traditional educational interventions frequently fail to achieve this goal. Behavioural science frameworks offer guidance to develop alternative types of interventions, helping to translate formative research and insights about the target population and behavioural determinants into more effective strategies. This paper outlines the outputs and decision-making underlying the five-stage process we followed to translate formative research findings into intervention activities and materials: (1) synthesising formative research findings into a creative brief to guide intervention development; (2) selecting behaviour change techniques (BCTs) to address key behavioural targets; (3) selecting an overarching intervention concept; (4) developing intervention content; and (5) finalising the intervention's Theory of Change. This paper presents our experiences and reflections on the intervention design process, using a practical example of a face washing intervention for trachoma control. The intervention was designed for delivery in the Stronger SAFE trial in rural Oromia, Ethiopia (ISCRTN 40760473).