I want to improve spriting and am looking for constructive criticism

[Driedmanjello]

So I make sprites online and I am decent and I want to improve. I make sprites of sizes generally 64 x 64 and higher. Any constructive criticism is great.  I have examples of my work below. I have a deviantART as well with a hundred other sprites at http://driedmanjello.deviantart.com/ Thanks.