Okay, what everyone said before me is good.
Work on anatomy.
Practice practice practice
and take it little bit's at a time.
However, if you're like I was and can't resist adding a bit of colour and experimenting, then I'll give you a few pointers.
One Vox on deviantart has some brilliant youtube videos on stuff like the basics of painting.
With painting you have to pay attention to shadows, which means lot's of practice looking at objects and studying the way that light moves. Your image loos flat, because there are no shadows or contrast.
Uhm. Basically, adding contrast and shadows and highlights can really improve the look of your piece.
Pleasepleaseplease DON'T use the dodge or burn tool. They look crap.
For now, pick a colour, stick to perhaps three fairly different colours until you have a strong sense of what's going on, then experiment with adding the many different colours you'll find in things like flesh.
It's a lot to work on, but don't worry! With practice you'll improve quickly. Good Luck!