Edit: Ninja'd by MatHey man! Welcome to DD, first off. Nice animation! I can tell you have a lot of potential. :)
I edited it for fun to try and make it flow a bit better:
This was only for fun, I'm not telling you to animate this way, haha. Just an example. I used all of your frames in it. It's a bit shaky, and still doesn't flow too nicely
There were a couple issues:
No foot placement (Foot placement is done correctly when the foot stays in the same spot unless it leaves or gets pushed from the ground)
Some easing issues (easing is slowing movements down after a speedy movement, or moderate, even slow movements should be eased)
Not moving every joint in every frame (you sort of "double framed" the movements. An object that goes in motion stays in motion. You also need to bend the joints more, dont let them be too stiff. When animating, try doing that movement yourself, then animate it how you followed through. Comparing these ideas make the animation much more believable.)
Shakiness and popping (when the stick figure goes down from that knee, the leg just pops into a straight line, and that just isnt right, lol. Always make sure that it goes together. There was a bit of shakiness due to static limbs as well.)
Body movement issues (When the stick figure completed an attack, you never really showed the effect it had on him as a whole. For example, that punch was pretty big, so his head should have went forward as well as his lower and upper body. And with the knee, try doing a knee with your back bent like that. It just doesnt feel right.)
All in all, man, this is actually not too bad! My advice: Check out some of the tutorials we have here and try and go off of those.
Best of luck