For beginners retopologizing a blend shapes 3D model, the key steps are: duplicate the base mesh, trace a low-poly topology with consistent edge loops, and test for smooth deformation.
First, duplicate your original high-poly base—this preserves the original blend shapes. Use tools like Blender’s Grease Pencil or Maya’s Quad Draw to trace a clean, quad-dominant low-poly mesh over the base—quads deform more predictably than triangles. Crucially, ensure every blend shape shares the same edge loop structure (e.g., a mouth loop in the same place for all shapes) to avoid blending glitches. Finally, test the new topology with your blend shapes and adjust vertices to fix stretching or tearing.
If you’re starting out, practice with simple blend shapes (like a basic smile) first—complex ones (e.g., a grimace) are easier once you master consistent topology. Using the original mesh as a reference keeps your new topology aligned.