Drawing hands is really a royal discipline, you have already understood a lot, it just seems a little stiff, which helps me, are my own hands as a reference (take the pose with your hand and you notice that it feels cramped and unnatural) also draw many hands in different poses again and again. What I see with you, the knuckles are aligned in a line, but they make a slight arc and it continues at the second finger joint. Be sure to display the shortening better. A good exercise for this is to draw cylinders from different perspectives. You can take pictures of snakes as references, instead of the body you draw a lot of cylinders on a string. I hope I could help you. Please write to me if the feedback helped you. Thank you