I suggest you check out Pixeljoint—coincidentally it’s down today for a server upgrade, but the community offers excellent feedback for new artists, and the tutorial section has links to some great resources. Pixelation is a great community with many experienced artists from the pixel world and demoscene. You’ll also find a couple of tutorials on an older site of mine, Studio Purloux. One is a general tutorial by my good friend Kevin Chaloux, an outstanding and highly regarded pixel artist; the other is my own introduction to manual antialiasing. That should be enough to get you started.