In this article, we report findings from a study aimed at developing the content and implementation of a manual for a research-based intervention on clinical supervision of mental health nursing staff. The intervention was designed to strengthen already existing supervision practices through educational preparation for supervision and systematic reflection on supervision. The intervention consists of three sessions and was implemented on two groups of mental health hospital staff. We present an outline of the manual and explain how the trial sessions made us adjust the preliminary manual. The effects of implementing the manual will subsequently be analysed in an independent randomised controlled trial.