Improvement...?

Left one does have a better sense of form. the middle one is a better sketch, but lacks refinement and is a bit messy. The one on the right is a large improvement.

I'll mention a few things; You're still look a bit like you're drawing contours instead of forms. In addition, a little research into clothing folds might go a long way; They do follow rules.

For the girl on the left, be careful of a few things - One is where you have hair that greatly exceeds the volume of the skull, or "Fran Fine" syndrome as I like to call it. Hair generally doesn't go far from the skull. Also, her eyes are still a bit on the big side. Have you been experimenting with eye styles? Even if you stick to anime, there's a lot to choose from, and you can always create your own.

The girl in the m iddle, the main issue is that it's rough and you're using too heavy a pen! Adjust your brush settings. You want pressure set to opacity so that in order to get hard black lines you have to push down completely, and if you draw very lightly you should barely be able to see the line at all. I find setting the softness to 0 and pressure to opacity and size helps in this.

For the girl on the right, I like. The proportions aren't too outlandish and her eyes and hair look about right, proportionally, for an anime character. Drawing poses with heavy foreshortening can be extremely tough. Keep at it.

Your drawing of SP-tan was also interesting; You still need to keep the eyes from getting too big, and there are issues with poses that are sort of "hanging in mid air", but your proportions are getting better (though her legs are a bit long).

I don't know if you do it already, but you should try drawing your characters without clothes, THEN dressing them. Clothing sits over the form of the body, and it kinda shows when you skip that step.