After seeing some of the other stuff in this thread my work looks pretty bad, but this is literally the first serious thing I've ever done in paint.
Do more. Do piles more artwork. Don't get all sobby over other people's work. Before you even notice, your stuff looks a whole lot better than the stuff you made before. (I've been drawing with MSPaint since I was 5 years old, you really notice the difference there.)
I recommend you to start practicing shading next. You have a big bucket of potential and I'm willing to see it spilled all over your work. Go get inspired, get to work, and return with content!