To improve my pixel art, I've been doing the #pixel_dailies challenge on Twitter pretty consistently from around November 2016. One of the first pieces I did that I really liked was this pic of DS9 from the Star Trek series of the same name. I used Graphics Gale at the time, but I've since moved onto Aseprite as I find its tools much easier to use.
I got a good reaction on Twitter and it was important for convincing myself that I had a future doing pixel art, and that it would improve with consistent practice.
Coder / Pixel Artist / Indie Game Dev