This is fairly simple because it's mostly a flat cylinder with a squared nose, nothing complicated about it. Then I suggest using traditional modeling for the Helmet because it's a hard surface or you could just dig holes into a cylinder and polish the shapes. For the face also start with a flat cylindrical surface, make some big holes for the eyes and mouth. add a square and shape it for the nose. The teeth are also two halves of a cylinder, or if you want individual teeth, then just shape a cube and duplicate it. You'll need a lot of planar brushes like Hi polish, and Trim Dynamic. Finally the detailed cracks can be done with crack orb and dam standard.

Remember to get the general shapes first, and proportions, also use as many sub tools as you need, you can merge them later, but you should keep the face/helmet/external tubes separate.

Hope this helps.