Well lets start with a compliment.
Your coloring looks nice, and I like the first set of images.
Now for some serious critique.
The girl jumping needs her butt raised a bit.
Actually I think both of them need their asses raised a little.
The left buttock is lower than the right.
You could also make the outline of the butt a little rounder.
Also, you should make the left torso a little longer before it goes into the hip.
The hand thing... Try making the fingers without so much differentiation between their sections.
Hands should also be the same size as the face.
The posing on the foreground girl is very nice however,
and you seem to have a good sense for dynamic posing in general.
There, please don't take any offense to what I say,
it doesn't mean anything,
I just pay too much attention to other peoples art while failing at my own.