I am pretty new myself, but I have a few comments to make...
When you are starting out I suggest doing bigger sprites. It takes a LOT of skill to fit in a lot of detail into such a little amount of pixels. My first impression when I saw it was that it was flat that is because you have flood filled great proportions of the boy, and then added a few darker pixels to the left hand side...I dont know what perspective you were trying to achieve with this, however the waistline still needs to be curved to show that the body does actually go round instead of being completely flat...
I also think the body is a bit too square...
My suggestion is to remember where the light source is and this will also make parts of the body lighter, as well as one side darker...look at other sprites with a similar perspective from yours and see how they draw them. Then draw some in the same style as theirs. Once you get competant with that, edit your sprites so that they fit into your own unique style...
Sorry if my advice is a bit confused, but I am starting out myself too...