Well I first learned how with a few tutorials. Specifically these helped me a lot:
[link] this one for actually making the pixel, and
[link] this one helped a lot with animation.
It's just a matter of being able to make out the basic shape of what you want, zoom out to look at it, and then fix where needed, and not to give up until you're satisfied with it. I'm not a very fast pixeller, if I'm lucky it won't take me three hours to make one. ^^'