Nice SB keep it up!
One thing that is noticeable in your older head-sketches is that you tend to make the skull sphere really small and the lower face very long. Mihail has pointed this out as well. You have become much better with your head anatomy, the mistake is not as dominant as it once was, though it is still here. A rule of thumb is that the eyes should be in just about the middle of the face (Not a very accurate rule, but ok for quick measures). In general just make the sphere of the skull bigger.