What exactly are you going for? I mean, these look like OK basic character drawings for animation or something.
Not super amazing, but then again this type of art is just supposed to tell us what something looks like.
Maybe some work on the actual lines, you usually want thicker lines around the outside for animation. I notice all your lines are the same width. And it looks like you used the line tool to do them instead of freehanding. It may just be me, but I think that looks a bit lazy. But, you know, that's just my opinion.
And work on movement. You can get that from any basic animation course. It's about making poses and items flow. That's what makes things dynamic.
If these are supposed to be stand alone pieces, as opposed to 'this is what the character looks like' ones, then you should work on your light and shadow. I notice you have no highlights. While this is standard in (cheaper) animation it isn't generally advised just for artwork.
For animation, we take a concept and simplify it as much as possible so it can be drawn over and over again. Though now thanks to computers we don't have to do that as much. It doesn't take hours and hours of tedious tracing to animate things anymore, so we can use way more detail.