I draw cartoons

[Chutzpar]

They're cartoons and I'm the cartoonist, so I'm gonna make things the way I want them to be.

You can't see it, but I'm rolling my eyes. A lot.

No matter how stylised you get, your work is still going to be a set of symbols based on real life, so you have to have *some* understanding of how real things are structured.

The main problems I see with your drawings are stiffness and a lack of depth. Both of these would be fixed with (wait for it), drawing from life.
Stiffness usually comes from not understanding how the body balances, and subsequently not being able to gesture convincingly.
Most of the time when you're on your feet - moving or not - your weight will be on one foot more than the other. Say that you're standing and putting your weight on your left foot - your left hip is then raised, because your leg is tense.
What do your shoulders do?
Usually they slope in the opposite direction, to compensate. Observe:



You're drawing people in sort of a naive way - their legs are placed evenly on the ground and their weight is pretty much dead-centre. That's why it's reading as stiff - nobody does that unless they're standing at attention.

So, why do I say your drawings look flat?
Even in the Thor picture where he's stepping forward, it doesn't look like he's stepping forward so much as his far leg is just sort of stunted- it's because there's no foreshortening.
this explains foreshortening pretty well. In essence, you need to think of the body as a set of 3d forms, don't just think in terms of their outside lines. It's especially important to think of the SURFACES you're drawing. Take Thor's leg, and think of the leg as a cylinder - if his lower leg is pointing away from us, should his laces really look so straight? What do stripes look like on a cylinder that's receding into the distance?

Oh, lastly: studying anatomy will always make things read better. Nobody's saying you have to have a total understanding of every minute muscle in the body, but a basic idea of their shapes will always pay dividends in making your work more convincing.
Check this guy out (not mine, I *wish* I was this good)
this artist's his work is VERY stylised and cartoony, but it's still based on solid construction. If you look at how he's drawn the arms, I doubt I need to tell you that they're not realistic. But they're based on simplified versions of the shape of real muscles, so they're convincing - and you only get that understanding by really looking at their shapes in real life, not just guessing at it.

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OH. While I remember, if you're into cartooning, you should definitely check out Preston Blair's Animation.

http://www.animationarchive.org/2006/05/...first.html
http://www.animationarchive.org/2006/05/...ourse.html
Check dese out.
Strictly you should only really use these for reference if you own the new edition and are using these scans to compare between the new one and the first edition (which had a lot of characters changed due to copyright claims from MGM, who Preston worked for)

I understand this isn't the style you're going for either, but the book is basically a course for learning the foundations of good character drawing that I detailed already, in a much more digestible form than more classical texts on the subject. Once you understand how to think of the body as a simpler 3d form, you'll take the headaches out drawing convincingly, even with more complicated or realistic styles, if you want to go that direction.