I see you used a base again. Speaking from experience, bases are more trouble than they're worth and they're a nasty habit that needs to be nipped in the bud. They can be addicting as they produce a decent piece for half the effort, but becoming dependent on them can hinder the expansion of your own independent abilities. That's not to say bases have no artistic merit period, but at the very least I must implore you to stop using traced bases as they're morally unscrupulous.
Now, your shading still needs work. You should study/continue studying shading and light sources so that you can understand how to make your shading look a little more "3D" I wish I had some good tutorials I could recommend to you for that, but alas, I do not. I do however have this awesome cell shading tutorial on hand. [link] Learning from it can really help you add that POP! to your shading.
I'm also kicking myself over here for not saving this really great tutorial on clothing folds when I had the chance earlier. If I happen upon it again, I'll be sure to shoot it your way, because it is really good. In the absence of this wonderful tutorial, I can at least try and explain clothing folds myself rather than telling your what's wrong and then leaving you alone i the dark.
To start, pants do not bunch around the thighs like this. The folds and creases in pants accumulate around the crotch, back knees, and ankles, essentially places that do a lot of moving and bending. The tighter the pants are, the more numerous and closer together the folds are, and the looser they are, the fewer and farther apart there are. This same fact can be applied to clothes in general. Shirts tend to bunch in places where there is more stress applied to them, such as the waist and armpits, and some shirts will bunch at the bottom. This also goes for arm warmers and long sleeves, with the areas of stress being the wrists and where the arm bends.
You did a good job with the folds on the red shirt! Her shirt is visibly looser than the other two and there are visible folds at her waist, and the shirt is bunching at the bottom.
Keep on practicing, and always do your best! You can do it!