The hidden curriculum consists of the unwritten rules, unspoken norms, and field-specific insider knowledge that are essential for student success but are not taught in classes. Examples include how to approach professors and prospective employers to ask for opportunities and how to gather information that is relevant to one's career goals. Students now informally learn these skills from more experienced peers, but not everyone has access to personalized one-on-one mentoring. We scaled up access to the hidden curriculum by creating a mentoring guide to advise students majoring in HCI/Design at our university. Readers have found it useful for orienting new students, helping older students who feel behind, and serving as a confidence booster. We synthesized our experiences into a five-step design methodology to help other students to create peer mentoring guides, with recommendations for 1) setup, 2) needfinding, 3) creating, 4) distributing, and 5) maintaining.