DRY BRUSHING

Here's how I like to dry brush details on an instrument panel, which provides a good example of bringing out detail.

First, I paint the IP black and let that dry.

Next I have a fairly fine brush... a 0 size... that I've trimmed the bristles so they are just stubs.

I choose a dry brush color.... for this example I normally use a very light gray. I dip the end of the brush into the paint in the lid.... just enough to color the bristles. I then brush off most of the paint on a piece of paper towel.

I then take the brush and begin to lightly brush the bristles over the raised detail. Since you've removed most of the paint, and will slowly add color to the raised detail, and with a light touch will mostly miss the surface of the IP itself. After a few brushes, I usually get the raised detail nicely colored, while the surface below is still black.

That basic technique will work for many applications, and a larger brush can work for bigger areas.

The trick, I think, is to have as little color as possible on the brush, and build up the color slowly. It's far easier to add more than to take away!

Hope this helps! 

One thing I've found particulalry helpful when drybrushing is to have the use towel I use to wipe the brush off when I am hand painting.  The towel has a texture to it and is colored from the paints I already have used.

I put some paint on the brush and then wipe most of it off.  I then go over and test it out on the part of the towl that has paint so I can see how heavy or light the drybursh will be.  That way I can adjust before goin to the actual model.