Students in introductory computing courses often struggle with fundamental computing topics and related concepts. Researchers have linked this with the challenge of conceptualizing the underlying mechanisms of basic computing processes and the multilayered interaction between the source code and the machine. To address this, educators frequently use notional machines (NMs) - simplified models of program execution that support students with diverse analogies, metaphors, diagrams, and representations. However, there is comparatively little guidance for CS educators on considerations and best practices in creating NMs for learning. In this poster, we present key considerations and design guidance for NM creation to support future CS educators.