Very nice job on this, but I do see a couple of things you may or may not want to work on. However, keep in mind that it's your art in the end, and you don't have to listen to me.
Anyway, your forearms are a tad long, so I'd try to work on that. One technique I've learned for doing this is to draw where you think the hand will be first and then connect it to the shoulder, and then draw a perpendicular line down the middle of the new line to divide into two parts where you would draw the two parts of the arm. I hope I'm making sense.
I really like how you drew the clothing; your folds and creases all look very nice.
Your necks seem to look a bit long and too forward. I don't have any tips for that other than studying real life necks.
Your coloring/shading/lighting are all pretty basic, but they do look nice, so I can't see anything to work on. Trying to improve it is always nice though.
One really noticeable thing is that your facial features are placed a bit too high and are pretty much identical to each other. Remember that eyes are generally placed in the center of the head, and you should arrange the other facial features accordingly (unless you wanted to place the eyes higher up as a form of exaggeration, but with that, you'd want to exaggerate the other facial features as well).
I also think it would be beneficiary to try and vary the placement and look of each facial feature to avoid drawing the same face over and over again.
Finally, I'm not sure on this one, but I believe this people you drew are female? If not, ignore me on this. Anyway, if they are female, you have given them very masculine looking jaws and chins, which don't really go with the general feminine look which the bodies suggest you were aiming for. Unless, of course, you were aiming for a more masculine look, which is perfectly fine too if you want.
Also, if they are female, keep in mind that gravity exists, so the blue haired one's breasts should be oriented downwards since she is upside down.
Overall, nice job though! Just got a couple of things to work on.