Welcome to Pixelation Olo. I admire your goal of trying to study and get great, but I wouldn't hold yourself to some timeline of when you'll be amazing. Anyone on this forum who I would consider, "good" has been drawing traditionally for a long long time, and have also spent a somewhat less amount of time getting good at actual pixel techniques (working with a limited palette, getting awesome colors and good contrast, AA, and tons of other pixel tricks to represent things with little colored blocks).
Anyway, onto the actual crit.
- I think one of the fundamental problems, that is very very common, is the palette. It lacks contrast, uses unnecessary colors, and makes the whole thing look flat. For instance, the blue is virtually a straight luminance ramp of even intervals. There sat and hue shift a little, but not enough to make any difference really.
- The shading does not define the form. You are not using shadows and light to imply the shape of the object, and because of that the object looks flat. This problem is very related to the first one, because it will be hard to get shape if the palette has no contrast. Because of this and the palette problems, it is hard to tell what is going on with the design. All the circles and triangles coming off the main shape, I don't know what they are. if the front triangle a gun or something to land on? Is it a ramp to get into the ship? You got to use the shadows meaningfully, you can't just throw them around the edge of an object then add more colors between the shadow and main color to make it look smooth. The shadows and lighted areas are what's gonna make the object look 3D.
I didn't really understand the ship very well so I kind of just removed a bunch of stuff. Of course you should keep it on if you like it, and if it makes the design better.

Essentially what I did was take your blue ramp and tried to add some contrast to it. I lightened the lightest colors, and darkened the darker ones. I also increased the change in sat between colors, and slid the darker colors more into the blue in terms of hue. I axed a ton of colors that wern't really adding anything, were just making the thing looked washed out. When you really reign in your palette then it will make the piece look crisp, and help give that "pixel art" look. Then I just got rid of all your shading and started from scratch. Also I did some rudimentary AA on the red and yellow lines. I still kind of suck at that so take it or leave it, but essentially I just tried to find a color between the two I was trying to mix (the red/yellow and blues).