Unlike text-based input to an intelligent tutoring system, a diagram is perceived as a whole state; the operation sequence is less important. Traditional step-wise coaching is not as appropriate in diagram-based intelligent tutoring systems (DITS). From two previous tutoring systems, StaticsTutor and Thermo Cycle Tutor, we propose cross-domain pedagogical guidelines for DITS. In particular, instruction needs to be mapped to a hierarchical understanding of the diagram, where each level focuses on different characteristics of the drawing. Also, instruction needs to address conceptual knowledge and procedure expertise separately. Some practical suggestions are described to achieve these goals, such as 1) different tolerance for error at different level of evaluation, 2) use of Q&A to resolve diagram ambiguity and 3) early loading of expertise that is important for avoiding difficult-to-fix diagrammatic states.