Woa ouch my eyes...
Will try not to be too harsh, but it is hard. I did similar skins once and I have moved on.
You need practice. I see loads of these skins too and all I can say is I avoid them.
First off try not using strong colors they look crappy and when ingame even crappyer. Shadows you need shadows and never EVER use filters as you did there. Make your use of filters subtle and if possible avoid.
Use brushes to skin. Set a low oppacity and boom you can make highlights and shadows pretty neet.
To get colors you can take examples of colors in allready existing skins. And if making a recolor or using parts from skins from other authors ask permission. When downloading skins you get a readme with and in there is most likely name and contact of the author. The standard skins in the game oh well, I can't say what the rules excactly are but everyone uses a piece or more of them all in great numbers.
Then you need to go outside, with a digicam if possible, and observe. Observe everything get inspiration and see how light affects objects like rusten cars. Walls briscks dust earth grass. Watch the colors and see what happens when you cast a shadow onto things.
If you have a digicam capture these things. Go home and look at alle the things and especially how real things are affected by light. Light and shadows are pretty crucial for making a skin.
Now draw something in photoshop, like a knob, screwdriver, lamp, anthing. Try to get it as real as possible this will likely improve your skinning and understanding of lightsources and how they affect objects.
My advice to you.
EDIT:: On help mastering Adobe Photoshop go here:
http://thedark.dk/photoshop/ a friend of mines site. He's talented with photoshop and learned most by using such sites.
