This guideline is intended to support the understanding and use of the PREPSOIL taxonomy and PREPSOIL self- assessment form for Living Labs and Lighthouses in the Mission Soil context. The PREPSOIL taxonomy of Mission Soil LLs and LHs is developed as a tool to support the identification and classification of initiatives aligning to the LLs and LHs principles that are working towards soil health in alignment to the Mission Soil Implementation Plan and criteria. The PREPSOIL self-assessment form enables initiatives to evaluate their maturity and alignment to the Mission Soil criteria and PREPSOIL taxonomy. By identifying areas of the PREPSOIL taxonomy needing improvement, the self-assessment form helps LLs and LHs initiatives assessing their progress and uncovering growth opportunities, thus becoming a versatile tool for various contexts, including reviews, milestones, or ad-hoc assessments. Delivered as annex to the related deliverable of the PREPSOIL project (D4.1 “Report on LL/LH taxonomy, identification and mapping feeding the online interactive atlas”, DOI: 10.5281/zenodo.13255005), this guideline is intended as an easily digestible and stand-alone document.