Total work of half an hour:


CnC is appreciated :3

Are you going for an anime style?
Because I'd suggest looking up some tutorials, watch it often if you don't already. Just try to familiarise yourself with it as best as possible. But the most obvious one is to simply keep at it.
And if it's anime you want, the head is fairly tall for the common anime heads you see.
If not, try and develop it into your own style, something more unique, don't try and force yourself into something you're not your best at if there's an easier route.
The hand could use some fixing, and the knee on the leg being raised should be bent further and higher up, the foot should be bent and on the ground.
I also wouldn't recommend a direct side view of the face, try body and faces from a 45 degrees angle away from the view point, it's very common in art, cartoons and anime. In fact, look at your avatar or mine, see how they're not directly facing the view point but not facing too far away? That's fairly common in drawing. Just try and keep that in mind.
I still like it, it's not actually bad. Keep it up, I see improve and a lot of it.

Tamen's cnc is pretty valid, but you're not trying Jan.
A 30 minute time-frame shows that you were eager to race through an idea and hope to receive proper critique for it.
I'm not gonna CnC this mainly for the sole reason that you should spend more time on your artworks, even if you're not confident about it.
That's the first step to improving; take your time.