I've been using this jam to try doing pixel art and I've been using the book pixel logic to learn and I've been finding it super informative. An example from the book that I read last night that applies to your art is that you have a lot of banding for you shading which is just where the shading perfectly follows the outline which can make the shape look blurry when you shrink it down. To fix it you can experiment with adding or removing a couple pixels from the edge or use some anti aliasing. But yeah I highly recommend the book it's only $10 on gumroad and there's a free preview that shows you a couple pages from each chapter and its written by one of the artists of cassette beasts