That sketch looks really nice

The first thing you need to get rid of however are the guides you made for yourself when drawing - the "bones" and body divisions that no longer server any purpose. Then (preferrably on a separate layer) go over the lines that really define the shape of the body - the arms, legs, and add more detail to the head. Is the character going to have any hair? What kind of eyes, and eyebrows? What about the expression of the mouth? Clothing is a little ambiguous too, as well as the object he is sitting on. Now that you have the rough shape set up correctly, strengthen it through clean lines :]
When it comes to color, dA itself has a lot of user-submitted tutorials for any applications. For the sort of loose color Shorai-san has applied, lower the opacity of your brush and build it up wherever you need with more strokes. Try to avoid using any Dodge&Burn tools too much, because they don't highlight or shade realistically. And always color on a different layer from your lineart, if you can :]
Either way, thumbs up on your drawing!