This will mainly be about colors:
What do you have now? You have a big picture, colored like a 90's fighter sprite. You use 88 colors. I suspect the way you color is by adding layers and approximating the color below by opacity. This is the wrong way to pixel, if you want to keep palettes under control. Handpick every color and make it count. It took me an hour to clean that sprite from 88 colors to 24, was this an hour well-spent? Control your art all the way through, so at the end you don't have to clean up.
23 colors, plus a spare for any transparent parts.
Even cleaned up: Every different item or surface is either RED, BLUE, GOLD or ORANGE. You make different ramps for these things, and you end up with lots of colors and a very un-unified picture. Even after minimizing the disparate ramps so they're 24 colors, it still looks less unified than I think it should. This could be further brought together down to the optimal 16 colors by optimising the usage, bringing similar hues a bit together, generally not having a BLUE VAMPIRE WEARING RED SHIRT, but a bluish-tinted vampire wearing a red-tinted shirt, under the cast of darkness.
16 colors
This still isn't unified enough, and now I have many colors from the face I could apply to the clothing to bring out highlights and such, so the full effect of this minimization in color usage cannot be seen at a strict color edit, but it should point you in the right direction.
Whatever program you're using, and whatever practises result in such huge amounts of color, if you want to become a fast, precise and adept pixeller, you need to change these things.
