Firstly, walk cycle. Seriously, take a tip from the pros, especially Mega Man. It's a simple 3-frame walk cycle but it looks great and I know I'm not the only person who still uses it as a guide. A walk cycle will make your run animation look much more natural.
Usually i start with a stickman and then draw the character on top once I'm happy with how the stickman runs. This really helps in terms of keeping the proportions the same and making the animation look natural while not spending ages fiddling about and redrawing stuff.
Secondly, detail. If you're going to use such a high resolution with not a lot of detail you have to absolutely make sure that the shape\outline of your character and the proportions are spot on. Seriously. Try reducing it to a silhouette and see what it looks like.
Third, practice. Lots of it. It's the only way you'll get better.
Also try some basic highlights\shadowing while you're at it, they can do wonders of wonders.
The body proportions are totally malformed, how is his left arm so fucking big in the OP pic? Also he has 2 dots in his hair. Also his bags have different colors. How do you want to animate this shit if no sprite looks the same?
Testicles in the armpit.
Also, make the name Penishands canon.
Oh, and you need to show us what the game is actually about. Hard to judge a game by one single sprite.