This document provides guidelines and best practices on the role of Honest Brokers and the advantages of the Open Science practices for this figure. Starting from a landscape analysis based on research in the literature, a use case scenario and interviews, it outlines the challenges Honest Brokers face, such as accessing reliable information, dealing with uncertainties, and how Open Science resources can enhance their effectiveness. The document distinguishes between various roles at the science-policy interface and emphasises the importance of trust, confidentiality, and impartiality. It also discusses the DIKW pyramid model, helpful in transforming data into wisdom. Additionally, it covers ethical conduct, communication skills, legal aspects, and the impact of AI tools. The guide concludes by highlighting the necessity of embracing Open Science practices and addressing the unique challenges Honest Brokers encounter.