"There is an urgent need for frameworks that prioritize fairness and inclusivity in the digital age. Data solidarity offers such a framework, aiming to achieve a more equitable distribution of benefits and risks in digital practices. Key to this approach is the concept of public value: the societal benefits that responsible data use can create while minimizing harm. A solidarity-based approach to data governance aims to maximize the public value emerging from the use of data and emphasizes fairness, transparency and accountability in digital practices. Translating these principles into action requires practical guidance. This guide serves as a tool for policymakers, businesses and civil society organizations, equipping them with strategies to implement data solidarity principles in their work. It provides actionable recommendations at all levels, introduces PLUTO (Public VaLUe Assessment TOol) as a structured method for evaluating the public value of data use and explores Harm Mitigation Bodies (HMBs) as a novel echanism for addressing data-related harms. The structure of the guide is as follows: it begins by introducing data solidarity and the concept of public value (Section 1) before offering a step-by-step framework for putting these ideas into practice (Section 2), with tailored strategies for local policymakers, national governments, businesses and non-profits. It also discusses Harm Mitigation Bodies (HMBs) and benefit-sharing agreements (BSAs) as policy instruments to promote data solidarity by reducing harm and ensuring the benefits of data use are widely felt." (Executive summary, pages 3-4)