Growing up in a Japanese household in Hawaii, and being my personal base style, I feel I have a good connection to what makes anime art appealing, and how it pertains here.
The hardest part about drawing in this style, is the economy of line. Since there are so few and very distinct lines, if you get placement or proportion wrong, it's very noticable.
The second hardest thing is the distortion (SD'ing) of head and body structure compared to other styles. Not only do you have to get it right with few lines, but get it right while SD'ing. Hard. :p
I see from your sketch that the facial portion, which always has to be right, is pretty good. I don't have any formal training, just practiced while looking at the best (Shirow, Samura, Miyazaki, Takahashi, Sadamoto, Akamatsu, Sonoda, Fujishima, Warren). Best of luck to you!