There has been strong interest in preprint commenting and review activities in recent years. Public preprint feedback can bring benefits to authors, readers and others in scholarly communication, however, the level of public commenting on preprints is still low. This is likely due to cultural barriers, such as fear by authors that criticisms on their paper will bias readers, editors and evaluators, and concerns by commenters that posting a public critique on a preprint by a more senior colleague may lead to retribution. In order to help address these cultural barriers and foster positive and constructive participation in public preprint feedback, we have developed a set of 14 principles for creating, responding to, and interpreting preprint feedback. The principles are clustered around four broad themes: Focused, Appropriate, Specific, Transparent (FAST). We describe each of the FAST principles and designate which actors (authors, reviewers and the community) each of the principles applies to. We discuss the possible implementation of the FAST principles by different stakeholders in science communication, and explore what opportunities and challenges lie ahead in the path towards a thriving preprint feedback ecosystem.