Warning, very quick edit, expect lots of jagged and twisted pixels:
Sprites themselves look very good, thou you need a bit more experience in animating.
Some very quick tips and vaguely explained on how to improve:
-Faster movement means less frames, and slower movement means more frames
The main probelm with your punch version, is that the motion of the punch traversing to the hitting zone had to much unncecesary frames, making the punch feel slower and without impact force, a basic fighting game attack usually has 4 stages: Prep time, launch, hitting and recover, the launch is usually the fastest meaning it needs less frames, thats where we usually put the blurred effect.
In animation, blurs are usually used to convey a movement so fast that even a single frame can not capture.
-Keep track of movement arcs
Pay attention to individual body parts and how they progres from one frame to another, in your gif, notice how his punching hand in the first frames, goes from stance position to being directly above his head in the very next frame, this is to much of a jump, so i added another frame in my version where you can see the hand traveling from those 2 positions.
-Keep track of the floor
try to constantly overlap your sprites to see if the feet jump positions to much, i usually do sketches of the moves and animate them before finishing the polished sprite, i make the adjustements before shading, once you feel the move has good flow and rithym you can shade it, its easier that way and you dont waste work.
Finally, become familiar with the 12 concepts of animation, there was this artticle about darkstalker animations, but i cant find it anywhere, the link is broken
here is an example:
Spoiler, click to toggle visibilty
Great work and good luck!