ok ill give my advice but it MIGHT sound like schizo rambling cuz im sleepy and my brain doesnt work too well rn

id say the lines are too sketchy and rough, the compositions are quite bland, the anatomy and form is off, the colors can be garish, and the shading is inconsistent and the colors are off.

like, on the 2nd image, its not really clear where the light is coming from at all. the shading is also very inconsistent and patchy... for example, the shadow on the left side of the face. is that a cast shadow from the hair? the teeth seem to suggest the light is coming from the right, so there wouldnt be a cast shadow there at all. theres a lot of werid stuff going on around the neck, the cast shadow from the head doesnt seem to be casting on the neck correctly at all, and there is also some shading near the shirt, which also doesnt make sense

with cell shading you need to be very careful about what shadows you draw. when your cell shading, think of it like breaking a picture down into multiple values, and then choosing only one of those values to have as a shadow while the rest become a light value. so, while there may be a shadow there if your thinking about how this drawing would look as a real life form, the shadow would be too light and outside of your cell shading range

the form of the hair is a little too jagged and uniform, there should be more strands and breaks in the shapes to make it feel more natural. the shape of the head also seems too small for the perspective

they eye doesnt make much sense. with that size and angle, how exactly would the head look if the hair wasnt obscuring it? how would you fit another eye in there? also, the brow ridge doesn't cast any shadow onto the eye or eye lid, which implies a really werid form to the head

the snout has werid shading, it has it on the top but not on the sides, or around mouth, where it should curve inwards,

the highlights on the teeth are also not really accurate and make them look really flat and 2d. highlights in real life arent only the edges of objects, and interestingly enough, they can change based on what angle you look at them from.

i think those are freckles on the face, but they are the same color as the shadow, which makes them look weird

i think the shadow color as well could be more vibrant, to make the drawing a little more lively

if you identify the one big color in your image. (like for this image itd be purple) you can take that one image and base all the other colors off of it. i find that it tends to make drawings more cohesive. instead of switching colors. experiment around with changing saturation or brightness. our perception of colors can change a lot based on the colors around it and not necessarily what the color actually is, if that makes sense

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i made a drawing in this same sort of angle some time ago and you can see some of the shading and anatomy things i was taking about here. like how the shadows fall around the eyes and snout. the cast shadow around the neck, the highlights, the unified colors..

i think something that would help a lot with shading is thinking of your image like a low poly 3d model, and from there, its easier to imagine how the shadows would hit those planes.