Well, what I see is a character that has decent proportions. It's asymmetrical. From what I can tell it's only two or three colors--Or four. The skin color, the outline color, the transparency color, and possibly the eye white. There are no VALUE(the shading) indication as to what the form is, so it feels flat. Let me see, I'll get my usual list of links, just a sec...
This one is a large list of general tuts you can choose from to help you out. http://www.andysowards.com/blog/2012/ 80-epic-pixel-art-tutorials/
This seems to be exactly what you're missing with this little guy here, the basics of value(shading). http://kiwinuptuo.deviantart.com/art/ Pixel-Art-Tutorial-Basics-196016837
And this last one should help you with the process of building up a tile. http://kiwinuptuo.deviantart.com/art/ Pixel-Art-Tutorial-Textures-203459613

This is a decent, and free drawing reference you could use to boost your skills at doing the human form. I hope it helps you calculate some aspects of the putting value to the human form. http://www.anatomy4sculptors.com/

Here is a site that might help you use help you see how professionals do their pixel work.http://www.spriters-resource.com/ds/luminousarc/index.html

Some advice for the fine tuning:
Try to make this one symmetrical, I natural things aren't naturally symmetrical but, you're not making a natural thing. You are making a representation of a natural thing. For this particular kind of base it should appear to be symmetrical.

Maybe rethink the proportions. Even though I said that were decent you could still rethink the proportions of the character. The head size and the body size.

When thinking of shading, or values think in terms of masses, shapes, lighting, and material. Also, to make the process of thinking of the shading easier use a grey scale of colors instead of a color. If you're not used to selecting colors and don't have a strong sense of color theory it will help you out to just do it in grey scale.

I'd say think about the tone of the game. You're visually translating how the game should feel to the player. Should it feel happy, sad, grungy, clean, scary, dirty, etc. Also, here is yet another link about color selection. Same person as the other two deviant art links. http://kiwinuptuo.deviantart.com/art/ Pixel-Art-Tutorial-Colors-184802567

You're welcome. Also, try out the free image software GIMP or Graphics Gale which also has a free version. The dmi editor seems to slow down a bit when you do larger graphic sizes.

http://cardgallery.tales-tra.com/tut.htm Translator or theres a english version somewhere i just cant find it.

http://abysswolf.deviantart.com/