When you are working towards a particular style, it's important to understand how the human body works to be able to distort it and make it still look correct. A lanky, fashion-type illustration style relies heavily on making a model look long and lean, but still retaining a type of bodily proportion.
I'd really like to see your process work to see how you are building your forms, but it seems like you are concerning yourself with the outline of the form rather than building it internally and then finding the final shape from the process. I think this is most apparent in the facial structure. You've applied an eyes/nose/mouth set without finding how it's built into the face. I think more work with realistic anatomy (and with live models, if you can manage to get some ^^) will really help with finding the form rather than trying to outline it on the page.
I'm actually surprised your teacher wanted to have you jump right into a style like that without understanding the form first... understanding how the body moves and fits together will also help with folds of clothing and how they hang off the body. Getting breasts to sit right in a shirt is always a pain. -_-;;;
I actually used to (when very bored, and I'm a bad role model for this statement) draw the students around me in my Art History and English classes... jeans make very interesting folds.
Great start though, I would continue at it. Lets see some more of your clothing designs. ^^
