My general rule of thumb for paint is: primer (because I use acryls), a very light layer of the final color over the primer (just enough that you don't see much of the primer any more), shading (personally, I won't use black unless it's on grey, I'll use a dark blue, black green, etc.) around the panel lines. You don't have to be neat at all with the shade. Next, I'll take a light color (maybe even a bit of white on the extreme hilights) and paint inbetween the panel lines. The last step is the trick. This is where I personally LOVE Vallejo's paints, and I'll explain why. The last step is to paint over everything again with a thin layer of the final (read proper) color. You want to paint just enough that you can very slightly (up to individual tastes) see your darks and lights still. Normally this takes several passes, and great care as the color will not build and not build and in my experience suddenly become too much. The reason I LOVE Vallejo so much is that they make a 'gloss medium' and 'matte medium' (think of Tamiya's bases). I mix equal parts medium and thinner and small amounts of paint (light colors I use 2 or 3 drops, dark colors 1 drop). This makes the final coat very easy to do, as it is so translucent due to the 'medium'. This being said, I imagine one could accomplish the same thing using clear coats at the 'medium', though I've not tried this. I hope that helps, as I'm sure you'll discover, it's all a matter of personal taste as to how much of the effect you want to accomplish, and of course it's a lot of experimentation. Nowadays I try to paint high pressure low volume, i.e. barely any paint coming out of the airbrush at all and just slowly build the color in an area. No spiders, no runs.
I hope all of that rambling helps.