Probably too big for a first piece! I'd suggest trying at half the size.
Pixel art is all about precise pixel placement, clean lines and details. The more pixels, the hardest it is ;)
Welcome anyway!
looks pretty good, but can be improved with a few small changes. I made an edit for you
desmond.imageshack.us/Himg717/scaled.php
Basically, I increased the contrast in the skin, nose, and eyes/teeth. I also added in some hue shifting. These 2 things give the image more "pop". It also increases the impression of form, and reduces the reliance on black lines here. With something this size, which is intended to be cartoony, I wouldnt worry about 1pixel thick black lines so much. By making them not 1 pixel thick, they will appear more hand drawn, as with a pen or real drawing utencil, line weight will be varied. For this peice, you could improve the black lines by giving them alot of AA. In my edit a gave some AA to the left eye. Some lines can be smoothed out a little. You have some unnessacery colors, for example I noticed you outlined the highlight on the nose with another color. This outline is not needed because its color cannot be descerned from the color its outlining. I couldnt even tell it was there at 4x. Generally, if you cant tell 2 colors apart at 1x, you can get rid of one of them. Either way, the way you outlined the highlight was using banding. You would want instead to use AA (though in this case just getting rid of the color entirely). Lastly, the perspective on the bottom teeth seems a little bit off. Getting a reference picture of teeth would help you fix that, though it doesnt really bother me in the context of the picture.
Thanks to anybody :D
I'm going to make something else, a few smaller maybe!