Upper halves of the arms are too long, approximately twice the proportional dimension they should be. The abs are also looking wrong. The face has some very obvious weebinitis, but I assume that is intentional. Also if your purpose is to practice, to learn then your better off not using any symmetry/mirroring tools.
I would suggest you get a good anatomy book. They can be pricey but they are well worth it. Also consider getting yourself a digital stylus and joining a dedicated art community, such as CGSociety.org for an example(rather than say deviantart which features mostly yes-men who can't give nor take constructive criticism).
As for your skills, it doesn't matter if you are dealing with pixel art or more classical/traditional styles. You need to understand the fundamentals of drawing and painting as well as anatomy to be able to draw a good looking image of a human.
