Common mistakes when sculpting humanoid 3D models include ignoring anatomical proportions, over-detailing too early, and neglecting topology (edge flow) for rigging.
Ignoring proportions—like misaligned eyes or too-short arms—breaks the "human-like" look, even if details are well-done. Over-detailing early (e.g., adding skin pores before fixing the torso) wastes time when adjusting the base form later. Neglecting topology leads to unnatural animation deformations, since poor edge flow doesn’t support movement.
For beginners, use a proportion guide (like the 8-head height rule) and focus on blocking out main shapes first—save small details for when the foundation is solid.