Many colored pencil artists have their own way of using the dry brush technique involving different papers and pencils. But this is the way I use it on the Ampersand Pastelbord with Coloursoft pencils by Derwent.
The Coloursoft are a bit more chalky than Prismas (Prismas being quite waxy), and when you brush them with a stiff bristle brush they behave a bit more like a soft pastel. Which happens to be the effect I'm after.
Here is a close up of an actual brush that I have used.
A pic of brushes that I bought in a packet at the craft store for about $8.00
I save my Prismas for working on Stonehenge paper where I also use the drybrush technique sometimes. That's a posting for another day.
This dry brush technique is what I used on the "Nectarines" colored pencil piece posted August 12th. The only drawback to this technique is that some of the chalky Coloursoft will brush off and you have to apply more layers. I don't brush too often towards the end of a piece....I usually result to using my fingertips to move the pencil around and to smoosh it into the board.