The anatomical studies are very helpful for you as an artist.
Other than learning from anatomical references, I'd say go out and bring a sketchbook and draw stuff you see around you. Draw people, places. whatever!!!
A lot of your work seems character driven, so I'd say to go out and draw some quick gestural studies of people in motion. Don't get too nit picky on what they look like, but get their overall forms.
Something I see in your sketchbook that is common with my older sketchbooks is an immense amount of head sketches. While it's not a bad thing, because a lot of expression is shown in the face, but there are two things I can see.
1. Most of your faces have the same expression.
2. Most of your faces have the same anatomical structure.
Not one person has the same shaped face. So be experimental on the overall shape of the face/head. I'd also recommend getting a book that at this point I cannot locate, so I'll have to let you know what it is when I do find it, but it has a bunch of different people (ages, genders, ethnicities) in a variety of facial poses that might help out.
One of my main issues, because I focus on the head as well, is that I don't give as much time on the rest of the body as I do the head. Remember that the head is a small part of the body and that if you are going to go all out on the head, that you should also use that much attention on the body.