Three-quarters of all mental health problems start before the age of 24 and yet outcomes from standard psychological therapies such as CBT are poorer for this age group compared to working age and older adults. More effective, acceptable, and accessible psychological interventions are needed during this period of peak onset. They offer the potential to change the longer-term trajectory for young people. A key challenge is how best to develop these treatments. In this paper we set out ten steps to facilitate translational treatment development that focuses on understanding and targeting psychological mechanisms. Each step is informed by theoretical underpinning, as well as consideration of the developmental context, and perspectives of young people, families, and key stakeholders. We introduce a public digital resource (https://aim.mhid.org.uk) which includes a searchable library of measures of psychological mechanisms, intended to encourage sharing of best practice and continued innovation.