You have a few colors that are used pretty sparingly, for example, the pitch black on the hands and mouth. You could get rid of them and swap them for some buffering colors. In other words, an additional shade to blend two colors together.
Remember to work on your pixel clusters. They're making the sprite look pretty rough, but I assume this sprite is still heavily WIP.
Watch the proportions of your character. The torso is too long, and likewise, the legs are too short. There's also the neck, but that's more the fault of bad pixel clusters than proportions.
Also, AAHH SELOUT
Edit:
I think Red's edit might have overdone his own point about detail and dimension, destroying the simplified, cel-shaded look you had going there in the process, but it's still a good point and something you might want to listen to.
