The base architecture must be strictly geometric (perfect circles, sharp triangles). It references the Futura/Bauhaus lineage of efficiency.
Introduce specific deviations that signal humanity. A slightly high crossbar, a curled tail, or a ball terminal. The font cannot be perfect; it must be charming.
Never black on white. Use Pastel on Pastel or High-Contrast Primaries (Yellow on Blue, Red on Pink). Text is a physical object in the world.