>>496314i'd say some lineweight can be arbitrary
try thinking about how deep the edges are everywhere and adjust the line intensity accordingly
it feels like you're forcibly trying to be too neat and precise at the expense of it looking like a man made drawing, get more line variation in there, it has that artificial look that can be off-putting a bit; try going a bit wilder and rougher, don't be afraid to miss one pixel, it can be detrimental in the end
i'd also comment on looking at how highlights work, they are inconsistent assuming the same light source and following the shapes, especially the pussy and ass is inconsistent, almost opposite, to the highlights of the top of the body
add at least one more tone to your hair, increase the value range; you need to think about each material and how much light they reflect; for example, hair is extremely reflective, yet your restricted value makes it look like it's less reflective than the skin, which ultimately gives the viewer the information that she's wearing spaghetti instead of hair
memorize a generic value range that will be the rough spectrum of values you are going to use, that will make everything easier as far as knowing how to tackle each basic material
remember that when shading, a round big object will have a ton of values because the object wraps back in space and so it catches some of the light from all the way back. so of course it is bound to have much more tone information than, say, the stomach. the ass is giving a flat look because it appears to have less value variation than the stomach, which is counter-intuitive
tone needs to be part of a hierarchy; you can get away with however many tones you want, BUT they need to be coherent with each other and respect their relationship.
i'd try to emphasize volumes more, they feel like they are lost especially in the legs; the human body is not actually 100% round. adding faint tone shifts will make the drawing look 100 times more believable
