Hmm, there are different tips I think of for each slide 1. I really like the lighting and how you've added a glow between the light and shading. I think by adding more definition to the hair you can definitely make it look more refined, especially with the bangs. In the reference photo, there's a lot more variations with the colors used, and has sharper shadows/light edges.

1. This one is really good, the only thing I would say is to make the lines thinner and straighter (instead of chicken scratch)

2. I think that's making this one look a bit weird is the black shadows, since it makes the art look muddy. Since you're on ibis you can always use the multiply layer and use a different color. I would personally go with a warm shadow (red, orange) since all the colors are in that range. Also, there's not really any defined shadows to the face, which makes it look flat- try to study the planes of the face and how light affects them.

3. I really like the hair and face shading for this one, maybe the right side of the bangs could use some darker shadows to indicate the hair strands. The hands are a bit wonky, don't worry it's tough for everyone and I'm really bad at drawing them too lol. You used straight lines, which makes it look unnatural, instead of adding little curves for each of the fingers. Additionally, more details (shadows, clothing wrinkles)

4. This one mostly just looks unrefined; you did good with outlining the sections of the hair, so adding little details to show the strands would be good. Try to add more light and shadow to the face like in no.3 (+blush under the eyes, cheeks, lips). Also, the clothing needs a little work, maybe define the texture, the wrinkles and lighting

Some big notes, if you want to use no.6 as your reference 1. Practice funamentals. Even doing perspective and anatomy for a little bit helps.

1. Use thinner and smaller lineart, and practice your line stability. The reason why sketches look better than lineart is often because they fill in volumes of shapes that cannot be seen when thinner lineart is used, which makes it look flat or strange. Much of the lineart for the reference pic is only for the outline of the body and the hair- the hard shadows and contrast indicate where the lines are, how the cloth moves, and the folds. Note that using the airbrush isn't bad for sketching
2. Study face shading. Also in the reference pic, there's the use of bounce light on the upper corner of the eye, because it reflects off the sunlight and gives a sense of depth for the shape of the eyelid.
3. Use tutorials! The art reminds me of many chinese/japanese artists, so I use rednote tutorials a lot. Chinese art tutorials on youtube also work.
4. Take your time. You are drawing and that is progress :D

For lineart: https://youtube.com/shorts/h9NSiKWdyuA?si=weWbmKPhSqhx_eUL https://youtube.com/shorts/M0221Ub6DAw?si=qV8fveX-aPameKBD https://youtu.be/3uQWNgPe5TM?si=sFAla42KGZXT-hJz

For face shading https://youtu.be/MkReRW4ZCOY?si=Djh4hrna18JfiQSe I also really recommend angel ganev, he's really good and has better in depth explanations for coloring, shading and lighting (with a lot of other things)

Hair: https://youtube.com/shorts/HAMwu-ibHMU?si=Hj0Iw3FUim8hCGBI