Select the single edge selected and extrude and merge the two edges marked red.
Now extrude the 3 edges marked green and merge the one marked red.
So here's the mesh for far, and its time for another mesh update Base Mesh 8.
Select and extrude the two selected edges scale them in like in the picture, this is going to be where the mouth is.
Select the 3 marked edges and extrude.
Extrude the marked edges.
Marked green, extrude the edge's again and marked red, merge the edges.
Marked green: extrude. Marked red: merged the edge. Mesh update Base Mesh 9.
Where its marked green extrude the edge and I've deleted a point to make a triangle, then where its marked red select the edges ready for the next extrude.
Extruded...
Marked green the edges extruded again, and time for another mesh update Base Head 10.
The next edges to be extruded.
More 3D Graphics: 
