In verlindens books about building armour he has a three step dry brush technique. overall drybrush: matt earth, khaki drill on lower hull and then second overall drybrush of matt forest green then highlite kahki drill. Can someone explain what excatly he is doing? Does he drybrush the whole armour or just the edges. If you add successive drybrushes what's the point of adding the first if it will be obscured by teh second and highlight DB. Any clarification would be helpful.

The idea is that with each successive drybrushing, you use lighter pressure and leave less paint. The final, lightest, drybrushing barely leaves any paint on the model and just slightly can be seen. The method works very well.

The first drybrushing is closer to the original base colour and everything gets a good going over to highlight all detail. Then with the addition of a lighter colour the second drybrushing is lighter and only brushed onto the more obvious detail and then possibly a third drybrushing with an even lighter colour to bring out the most obvious detail. The idea of these different tones is add depth in the overall picture. This effect, when worked properly is very effective, but has a tendency to be overdone as well. The arguemnet between realism and artistic license is brought up again and again here. 1.5 years ago when I started modelling one of the most important lessons was good drybrushing. Now its the "in thing" to have as little as possible as its not real. I guess a lot of it is up to your own individual taste! I personally like a little drybrushing and like the effect, but try not to overdo it either!

I have used a simular technique on figures. Skeletons I have done come to mind. Using Black then tan then a yellow and finally a white. Each time leaving less paint. The effect was very realistic. If you have the time and patience its worth it.

Layering paint has more effect then might be supposed, but the application requires quite a degree of sublety and control at small scales. You can get an idea of how it all works if you check out some books on fine art oil painting.
For example: Most of the well known 'old master' paintings i.e. Leonardo Da Vinci's Mona Lisa etc, are created by painting in many layers to duplicate the effect of the blood's colour below the surface, and muscle groups showing through the translucent skin, rather than just painting a flesh tone. If you ever do any portrait painting with oils, you'll appreciate how well this works. You can employ similar tachniques to replicate many things, not just skin.
Another example of how this can work: Ask your wife/girlfriend about 'green foundation'. If she uses foundation with a green tint, you will learn that it has the effect of dulling down the skin's redness and flattening the tones overall to produce that milky, smooth complection so beloved of women the world over! Essentially reversing the technique artists in the previous example are using.
You see, if you thought your wife/girlfriend couldn't help you with modelling, you were wrong LOL!
If you are bored anytime, try experimenting a bit on some scrap plastic or card with paints, add/miss out various dry-brushing stages, change opacites/colours. You'll be surprised by how things alter.
Incidentally, I personally think a lot of Verlinden stuff is actually really badly painted by the way, especially the figures, but that's just my opinion!