While starting small is a good idea for new learners, you may be starting too small. Having to fit an entire character into an area that small requires a lot of shortcuts and fancy tricks that take a while to pick up, so I'd recommend you go with simpler, larger images, such as 32x32 tiles or something like that.
As for those sprites, the first thing you should do is eliminate the black outlines. In a sprite this small every pixel counts, and the outlines frankly waste a lot of that space. It could also do with some shading, even if you have to stray from your color limit. What really confuses me is that the only part that is shaded is the shoes, which are maybe the least important part of the character. You could use a solid color for those and put another on the body, or even use their highlight as a shade for the skin.