Are you good at sketching with pencil and paper? If not, I recommend dropping pixel art for a few weeks, picking up a good book by Betty Edwards or Andrew Loomis (both can be found as pdfs online), and filling a couple sketchbooks.
To make good pixel art, or any other kind of art really, first you must learn to see shapes in a particular way that's not intuitive for non-artists. It's a bit hard to explain in words, but if your mind hasn't learned that trick, your shapes will always come out wrong and you won't know why. Sketching allows you to learn that skill quickly and easily, while pixeling has so many distractions that IMO it's almost impossible to learn from pixeling alone.
With the right approach, as described in the books I mentioned, most people see obvious and major progress after just a day or two. I'm not exaggerating at all, it took me literally one day of sketching with Betty Edwards' book to go from "I can't draw, it must be genetic" to "I can draw anything right if I look hard enough".
This might be oversimplifying it, but I think there are basically two kinds of people - maybe not people, but dispositions? states? Anyway - those who see/process/comprehend images in terms of shapes, and those who see/process/comprehend images in terms of light and shadow. Not that you can't be artistic with one approach vs another, but when it comes to what is ostensibly drawing or sketching, especially with a constrained economy of space ala pixel art, it's very important to work in light & shadow rather than shapes to impart something identifiable. For example, I sketch terribly. But if I force myself to do pointillism (no strokes, only dots), I can't help but work in terms of light/shadow. My "pointillist" sketches are 1000x better than my unconstrained sketches. I haven't had much luck with Drawing On The Right Side Of The Brain yet though. :/
The Loomis books are especially great and a must read for any figure drawing/painter/pixeller. However, if you start out with low-res pixel art (like a super mario snes sprite) then you don't really need to understand form at that level.
I can confirm this. I struggled a lot with making pixel art because I was trying to draw the outline with pixels and would always fail (except for rectangular inanimate objects like boxes and similar).
Then I tried to sketch first and it worked great. Here's the process:
1. draw by hand on paper
2. scan it (I take photos with my phone)
3. scale it down to the size you need
4. draw the outline (make sure two pixels do not touch except diagonally)
5. color with base colors
6. add shading
For steps 5 and 6 make sure you pick a consistent palette beforehand. Something with limited set of colors (say, up to 24) works best.
P.S. You can check the graphics I created this way in my Twitter feed (@mbabuskov). Look for the horse-shaped robot and the spaceship images and see how those look way better than other stuff I drew earlier.
With all due respect, I just looked at your pictures and it doesn't look like you're sketching right. Like, they're "ouch" level bad, 1 on a scale of 1 to 10. Sorry.
My best suggestion would be to actually go through some exercises in the books I mentioned. You should see massive improvement within days.
To make good pixel art, or any other kind of art really, first you must learn to see shapes in a particular way that's not intuitive for non-artists. It's a bit hard to explain in words, but if your mind hasn't learned that trick, your shapes will always come out wrong and you won't know why. Sketching allows you to learn that skill quickly and easily, while pixeling has so many distractions that IMO it's almost impossible to learn from pixeling alone.
With the right approach, as described in the books I mentioned, most people see obvious and major progress after just a day or two. I'm not exaggerating at all, it took me literally one day of sketching with Betty Edwards' book to go from "I can't draw, it must be genetic" to "I can draw anything right if I look hard enough".