Some things!
girl in green jacket:
-Her jaw line is too long. When the head is viewed in profile, the ear is closer to the center than it is to the back of the head. If the ear is drawn that far back, it kind of gives the impression that the back of her head is missing.
-Shortening the jaw line will emphasize a few other problems on the face. The shape of the eye is too oblong. Take in the left side a little bit. Additionally, the angle of the chin is too severe, and the underside of the nose is not severe enough. (Not the best examples---but the line of the profile is closer to "}" than it is to ">").
-I would try doing the jacket with a single, solid outline, rather than many sketchy ones. Striving towards a more economic use of your line is a good thing, and using a single line will put pressure on you to give concrete definition to things that you're only approximating with the sketchy lines. That said, sketchy lines definitely have their place, but my personal preference is to not have them in the final product.
-Finally, perhaps most importantly---don't shy away from drawing hands! they can be a lot of fun when you get the hang of them.
girl in purple:
-needs shoulders!
-eyes too far apart
-figuring out a way to create the background elements without resorting to a pre-made brush is the way to go here. the lights and stars are way too loud.
Also: what Jeph said. Boo crafty photoshop tricks! Hooray drawing from life!
edit: just re-read this and have to emphasize that I do not mean to come off like a jerk here.
