The first art is a little messy, I think there was no sketch before the inks? I dont know Im just guessing by looking at the line, try to have a pencil sketch, something that you thereafter will ink and then errase that sketch that was below, this way you will have a better structure and you cold have a more clean result.
The line is something you need to work on, that will separate you from the amateurs, if the line is clean, and it has some weight to it, like bolder lines on the outside of the drawing but thinner lines on the inside detail, also that a curve or a straight line renders as a single line, not a composition of many lines that create that curve, is really hard to explain just with text.
On the second art, apart from what enalya mention, what will take you to the next step is shading, try to be as smooth as possible with shading, try to get some tutorials in youtube about pencil shading and that will take you to another level, use the same technique of creating a sketch, do it with some 2H pencils, that are super light and dont draw any hard, try to be as transparent as possible with the sketch, then use 2B for the basic lines and as you go darker in shadows use darker pencils, like 4B and 8B for absolute dark parts.
