As I've seen in your drawings, it seems that you are trying to copy the forms that your eyes see without a structural base, loosing the whole view of the figure and sometimes, the correct proportions. May I ask in wich time do you drew the poses?
If I'm correct, you should try to "relax" your hand with short poses. If you are not already confortable with 30 seconds poses, you can try to do the 1-2 minutes ones. Doesn't matter if you don't get visible results at the beginning (I mean, it's really possible that you wont draw an entire figure in this interval): the idea is to put you into the right focus towards figure drawing.
Another thing that I see is that your sketches aren't very clean. It would help you to define the figure with less lines. In this way you will make your brain take a decision and construct a more solid idea of anatomy.
If you haven't seen the site's tutorials about figure drawing yet, they would be very helpful and more accurate that my opinion.
I'm not a professional, sometimes I struggle like you but these are advices that have helped me and continue to keep in mind them when drawing.
Hope my answer will help you :)
EDIT: when drawing hands I try to separate them in three forms: the palm, the fingers and the thumb. The lenght of the first two are the same. The structure of the thumb is quite different (roughly a short spoon), so you have to pay more attention to it and better check the anatomy if you have any doubts :)