Maybe I should take a break.
(Obviously incomplete. The braids looked nicer before I shaded them, I swear.) How do I fix the left hand?
First thing I notice is that she looks like she has depth to her body, which is a big improvement over what used to seem 'flat'.
Then, I notice the left hand's thumb should be on the outside of her body since the palms a facing up. A simple way to double check is to simply take your hands and put them in front of you both with your palms facing down. You notice the thumbs should be pointing toward the body. Now if you put your hands with palms up, you'll notice that the thumbs point outward.
But besides that, that looks like an extremely uncomfortable position for the left arm. Try doing it yourself. I'd say try looking up some basic martial arts stances for good reference. This also might help the right hand from looking like she's fist pumping the air. Maybe rotate the wrists more towards her face (so we don't see the whole front part of the right hand - the awkward part), and then tipping the wrists a bit forward, almost like a flexing pose.
Your ears also seem very out of place, and not integrated well. I had this same problem with the Kyouko and other Rin pic of yours.
You've been improving a lot though, so keep it up!