Hey Ikrus, I see this SB is brand new, welcome to CA.org!
From a first impression, I think that working on your line quality at this point is very important. From the face, the little...teddy bear monster and the owl, it's evident that you're using multiple, indecisive strokes to produce your line, whereas it's more pleasing to the eye and also quicker to create broad, decisive strokes. All in all, don't be afraid to make mistakes. Grab a sketchbook and try doing line drawings of inanimate objects from life with a pen(pen is unforgivable; you do a stroke and thats it. And no, no whiteout) using clear lines instead of a line made of small stroke clusters.
Either way, you'll be practicing that a lot in life drawing wherever you're going to study, but it's always good to be prepared.
That seems most important to me right now, but as for shading I'd like to give you a few pointers too. Try shading directionally or in a circular fashion, as I can see from the the face drawing that the shading is muddy. if light is hitting her face from the right, shade left side of the nose with horizontal strokes as to create the ilusion that light is hitting from the right. And finally, make the shaded a solid tone instead of a cloudy block of several shades.
Just watched this video of Nate Van Dyke on youtube (http://www.youtube.com/watch?v=ksIsbwHqeks ), it inspired me to work on my line control. Wasn't till about halfway through both of these that I figured out what I was going to draw.