You'r work doesnt have depth at all, you need to increase the contrast on the things that are closer to the viewer, make it darker and more saturated, and do the opposite for whats farther away from the viewer, i would study loomis heads n hands book, you need to learn about the plane changes in the face to make for a more succesful piece.
hope it helps.
-We are what we repeatedly do. Excellence then, is not an act, but a habit.
-Some are born great, some achieve greatness, and some have greatness thrust upon 'em.
i like the direction your headed, i see potential that you will continue to get better. if i were to try to help, id say focus on your work from a distance more, i see you put in nice,small details, but im saying put in larger details to give it more form, so it doesnt look so flat. i hope i have explained my thought clearly and it helps you. keep it up!
I learned that before going into digital all the way one must first know the basics.
By that i mean, grab the cheapest paper you can find, a pen and start drawing everything you see.
There are very good reference websites around for human anatomy, and other subjects.
Draw daily and ALOT from life, first focus on proportion and confidence in each line you do, then go into value and all the other fun subjects once you are far more confortable with the basics.
But never forget to keep working on the basics!
Theres not more to it than that