Will it be through experiences on the job, or a formal training intervention, or through the support of a coach or a mentor? Help them with this by outlining what the organization is able to resource. Ask them to write up the learning targets, with ideas of how they will achieve them. Ask them to think about what resources they might need (time, money, support from you/the organization) and then ask them to set a realistic time frame for achievement. Moving forward you should encourage them to keep a record of their learning on a regular basis (ideally every month). Encourage them to regularly monitor progress against the development plan, removing those areas achieved and adding new targets for learning to support their continuous professional development. Finally, find a mutually agreed time when you will meet to review and discuss progress against the development plan.