Dude you really really need to work to reference material. You're always going to have problem areas with characters in terms of proportion unless you're a)very experienced or b) working to ref.

It's much more difficult than it looks getting a character to look right. We see people every day and for that reason, we can spot flaws very easily. Even if we don't know exactly what the flaws are, even the most unartistic person can spot something that doesnt look right.

If you work to ref you leave little to chance, and your models will instantly look better, and from there its just practice. Even better - study some simple anatomy and basic 'drawing the human form' rules. For example: eyes should generally be an eye's width apart, average human head is 5 eyes wide. Human body is average 8 heads high etc etc. Good luck & have fun