I've recently have been trying to get smoother movements out of my sticks since im transitioning from brush to line tool. I'm aware this is quick and kind of unfinished but I put this together real quick to see if the movement are smooth enough. (keep refreshing page after the animation stops to keep viewing it) and tell me what you guys think about this. Keep in mind im a beginner, Thanks in advanced for the feedback!

Animation: http://sta.sh/01hd0bk2w8fq

You need a lot more frames, guy. Try doing a three hit combo, but add so many frames that you give off the effect of slow motion. If done correctly, the movements will flow smoothly from one to the next.
There is nothing smooth about this animation :(

Try making a keyframe every 2 seconds, each having the end pose for the punch or move the guy is doing.

Between these is where you'll work on smoothing and animating it. if you're at 24 fps, you can make a frame every 2 frames (effectively 12 fps), and just work on easing and really emulating how you'd punch, how you'd throw your back and shoulders into it, and varying the speeds between each frame into a thrust. make sense?