I’d suggest looking at the shapes and the negative spaces first. Pick out the basic shape of the head and build those. don’t worry about eyes or nose or any other detail. Once your happy with the shape. Subdivide if need be, but start to work on the next set of shapes. The nose and mouth area. Maybe sink the eyes area in a bit. Basically your working in stages, building up the model bit by bit. Kind of working in layers in a way.
Start with good background image. Here I found good side view of ratchet. So built basic shape out of cube. The muzzle feature was extruded out from front lower face.
After that, I started on detail by creating loops around mouth, eyes, and where ear meets the head. Go from simple to complex. Building general shape with least amount of vertex. Once you create too many vertex, it becomes difficult to rearrange them.