Well in my opinion, the way the Loonatics has been draw is sort of similar to anime styles. Obviously you need to work out the proportions of the shape for each part of the body. For example, the legs are half of the overall body length and so on. Then you just have to work out the rest of the features of the Loonatics like Duck's and Rev's beak and the furry cheeks of each character.

Whenever I have problems with drawing cartoon characters, I dive headlong into figure drawing.  Getting the basic foundation of the human body in your head makes cartoon characters easier, because all cartoons are based on real life in a way. 

It's always good to remember that while all the characters have relatively compact proportions, their physical types are all different.  For example, Ace is about the same height as Tech, but has broader/more muscular shoulders, Rev is taller than Duck, but Duck has broader shoulders and a shorter neck, Slam has a very large, beefy build, and so on and so forth.  Ace and Lexi may have similar constructions, but there are important differences such as Ace usually have a bigger, broader mouth with more pronounced teeth to make her look more feminine in comparison.  It's your choice whether you want to be perfectly on model or not. 

Try using different drawing styles or practice drawing parts of the Loonatics' bodies seperately (like only draw the head one day, then a hand tomorrow on another piece of paper). Also practice is the key. Good luck!

Okay since i did Steve very well then i will do the others.

Yesh! =3