U doin things up-side down
DOOD, MY MOST IMPORTANT ADVICE EVER TO YOU AND ANY ANYONE ELSE INTERESTED IN DRAWING!!!
Never EVER start with the simple stuff EVER!!! You absolutely MUST learn the complicated stuff first. Do not start with simple line art and/or anime it will ruin your drawing, and I would know cause I went about it the wrong way, thinking that i wouldnt need to draw realistically to be able to improve. On the contrary realistic style drawing actually helps with cartooning and simple line drawings like the ones used in anime.
Instead of drawing this stuff that u have drawn I would recomend you to get a book called "An Atlas of Anatomy for Artists" it is kickass (or any other GOOD anatomy book), and learn how to draw AND shade every position of every muscle in the body, and the entire body as a whole. Then use referrence to find out how everything looks when the skin is over the muscles (this is very important step).
Also dont forget, to let your hand flow freely; dont constrain your lines and things will look much more natural.
LAST THING: A lot of your fully colored characters aren't at all balanced on their two feet. Study how the human body compensates for leaning, and how it reacts to falling and etc...
Thats about all so g'luck