To rotate normals on 3D models effectively, start with your software’s "edit normals" tool (e.g., Blender’s Normal Edit mode) and check face orientation first to fix flipped normals (which cause black faces).
Use axis constraints (X/Y/Z) for precise control—align normals perpendicular for hard surfaces (like a cube) or blended for organic shapes (like a character’s arm) to get natural shading. Avoid over-rotating, as this breaks lighting.
If you’re new, practice on simple shapes first—this helps you learn how normal rotations affect renders without complexity.