Hi iSpring,
This is interesting. I'm wondering about the context, what is this for? I makes me think of an old RPG with front view battles.
What program did you make this in?
One of the first things I notice is there's a lot of blank canvas space. First easy improvement you can make is crop that baby down to the essential space only. In Photoshop this is easy with the crop tool. If you're in something else, it might be under canvas size or something like that. I think you've got about 150px x 150px here.
The reason you don't want so much blank space is that it makes the file size larger, and the art of pixels is all about working inside tight restrictions.
You might want to also check to make sure your screen is calibrated, because everything looks a little dark. For example, I'm not a fan of the skin tone, it's far too yellow. Here's what it looks like when it's brightened up some:
Cheers!