I dont really do all that much, just try to imagine or related things to the way things look in life. For skin, I select a color that makes sense, and for the shadows on the skin, I change the color diagonally down to the right on the color scale till it gives a good contrast an put it opposite of the light direction. If I dont think it contrasts enough Ill burn it a bit and blend it in with some smudging. I guess the best tip I can give is not to be afriad of certain areas being too intense. When I started out, all my colors looked kind of dull because while you could see the shadows, they really didnt look like shadows. If you go outsite and its a really bright day, or there is only one sourse of light, the shadow the light creates is usually strong, not just a tad darker, to thats the principal I followed. Same thing with clothes, pick you cloth color, and a little light refraction, and anything else that you think would be overshadowed, just burn it a bit. And know when to have it faded in or an immediate contrast. All of that info you can get by looking at light hits the clothes and stuff like that. Apply a little bit or reality just to get an Idea.
As far as why it was a weak attempt, Kakashis black shirt is one of the things I could have done better on, I only had black, and the light part, but since the cleans I was using werent from high quality scan I didnt bother with that and wasnt really trying to get anything perfect. It came out fine, but even then Im still a tad dissapointed with the kakashi cover. If anything I liked the way the book came out, but was dissapointed with the gloves, especially cause the cover was kind of odd and an unidentifiable black thing over the metal plate. Im just waiting for batanga and vhea to come and show me up. Probably DD as well. I only use photoshop cs2, but sometimes in the beginning I would use bryce 5 for sky backgrounds. Bryce is a 3d landscape modeling program that Im not all that great with.
I was thinking about doing the kyuubi page that nytro did as well, but once the hq comes out. I was kind of debating on whether the black balls should be a flat color, or super smooth and reflective. What do you guys think?