I would recommend you find a good tutorial, make a test skin, and then use empathy to improve it. ie: where would the light fall? Also to not make a bland skin, try different shading types to show a difference in cloth or metal.

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I just...

I cant explain it, its comes naturally for me

I cant put how to do it in words, nor how to do it with pictures...

just, learn, hon your skills, and become the master of skinning

"Art is entirely up to the artist. No art is ever ugly, i can splash paint on your face, mix a few colors till its pitch black, then paint a black raven on your nose and call it a masterpiece." ~Wise quotes i think up on the spot, that are slightly wise.

Enyways, when you shade you can do it simple, beguiner style: Color> Same color but darker> and get darker as you come to an end.
Thats all i could say, from there practice alot, unless you have natural talent like me (no pun intended), then learn how to combine the nearest color but different color, also known as dithering, which could also reduce gif images, and also try not to have colors that are too unsaturated if your going for a more cartoonish, SIMPLE skin. Guess thats it, if you would like me to make a skin for you then please post your skin requests in my thread:
taking-any-all-skin-requests-t228718.html
Thanks! =]

Your last skin looks pretty nice with that shading. Do you want to know like detailed shading, or more of a cartoon-ish shading?

When I shade, I try to follow normal contours of the body and clothing. I don't like overshading, so my shading seems to lend a cartoony style. For example, your back slopes inward, toward the front of your body, unless you have a hunchback. In this case, the shading would go from light near the shoulders to dark near the waist. For clothing, ridges are lighter and valleys are darker. I tend not to overshade the skin, using only one or two colors to shade the face and bare arms.

That is a good compilation of guides, but remember, everyone has a different style of shading. Try out different types, and you will eventually get one that you like.

Here is a list of skinning tutorials, just scroll down to see it.

http://www.planetminecraft.com/forums/the-official-pmc-skinning-guide-compendium-t91418.html