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".