If you'd really like to improve on your art, perhaps you should take to looking at references. Or even some tutorials. There are several websites that provide them, though I don't have the time at the moment to look them up. Otherwise, I would've provided some links for you. However, keep up the good work and always practice.

Looking at your art I see that you're having some trouble figuring out proportions while drawing and also eliminating the stiffness of your poses. That's usually caused by not being loose enough with your pencil.
You should try some exercises for this sort of thing, like keeping your pencil on the paper for as long as possible drawing curves and tracing over them multiple times. This is also an exercise to lighten your strokes on the paper thus making it easier to fix small errors and relieving the stress of getting it all right the first time.
You should also try gesture drawing which requires your to indicate a pose or shape in a few quick strokes. This usually helps you with starting a composition, easing you in to the details instead of throwing your right in, it also helps you put your ideas on paper in very few quick strokes.

There is a channel on youtube that really accentuates these techniques in some of the podcasts. Here it is they may be long but if you find the right ones that involve figure drawings it'll give you a good idea of how to loosen up while drawing.

Hope this helps =P