Here's how I solved it for mine. More or less the same base.

that's some nice subpixel work! 

yes, like that, his arms are looking wierd now.
you should try not to mirror so much aswell.

Yeah, that was a problem the old pixelation used to have and one that I blame the current pixeljoint. The background just doesn't flatter the pixel art and that's a problem on a forum used for showing that art. I remember posts on old pixelation going "I added a background because otherwise it looks really bad on these colors".

I have a problem posting my art on pixeljoint, because the default background is so damn white that it makes all my art look ugly. I realise I can change my user theme, but that's not how 80% of the PixelJoint members are going to see it anyway.

This is exactly why I have used the pixelation theme on pixel joint for a long time.

no, using your canvas as if painting a picture, using a bigger brush. then refining it.

but at the size you're working it's too small too get away with it not being stylized, the thing about spriting for a game is to create readability. Therefore it is much more difficult to draw in as much detail as the sprites you've just linked to. Could we see some of your other graphics? because I much prefer the edits with the larger helmets to the version you are currently working with.