Hi,
I took a look at the piece with the sitting girl, and I noticed a few things I hope you'll be happy to see.
I d-loaded your pic and marked up a few things to make the crit easier to follow, I hope you don't mind.
I'll explain my notations as I go;
i. The thing is the pose really, and actually this is a hard one. There is really two interpretations of a pose like this, the first one is that she is relaxing, sitting on her heels. The second one is that she's crouching, which is a more dynamic and unbalanced pose. Her right leg, the marked one, is crouching, but her left leg is relaxing. For the rest of this crit I'm going to assume that she is supposed to be relaxing on her heels.
ii. This is not about the arm as much as it is about the space between her leg, torso and arm. If she is supposed to be resting her elbow on the leg it is soon about to slip of and she'll fall backwards and to her left. To avoid this the line of balance for her head+torso and arm should be aligned with the line of balance for the whole body. I realize now that I didn't sketch the line, but you should still be able to see what I mean by looking at the triangles I drew under her arm in B.
iii. The shoulders and breasts are foreshortened a bit strangely. Look at the red lines in B. The red vertical line to her left is longer than the one on her right. I know you know why this is wrong, but stuff like this always happens when you work on something hours on end. Do you flip the canvas as you work? It helps a lot, I do it like every ten minutes when I paint and draw digitally.
iv. What is she grabbing with her hand?
v. Awesome renderin', but it detracts from her face. Still, it's awesome, just awesome...
Alright, so there's three (four) more things I haven't covered yet. The B part of the img I use there's kind of a redline going on, only that it's green. I only used it to pinpoint the errors I knew was in the pose, But you don't need to use it, unless you want to.
Second, why didn't you paint the top of her hat? I know you can do it splendidly, I mean you drew everything else so well. There's no excuse for not drawing the whole thing when you draw digitally, there's not like there's a limit to the space on the canvas right
Third, you render very well, but the overall shadowing is a bit, forgive me, random. Unless you really know what you are doing, use only one lightsource, especially when it comes to cartoons, manga, anime and so on (because the forms are so simplistic it's hard to get a 3d effect with more than one source)
And the fourth: I hope you didn't find the crit to harsh. The crit is extensive because I feel like you have the potential to get what I tried to say and use it to improve, so I'll hope this will be useful to you

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