This simple technique highlights raised details and heightens visual interest. Dry-brushing mimics the play of light on a subject. The keys to good dry-brushing are starting with a flat finish so the paint adheres better and avoiding overdoing the effect.
The dry-brush color should be lighter than the base coat. For instance, on this 1/35 scale Panzer IV painted with Tamiya German Grey (No. XF-63), Ocean Gray 2 (No. XF-82) works. You can lighten the base color, but going too light will make the model look frosted.

Dip a stiff, flat brush — an older brush with slightly worn bristles works fine — into the paint and remove excess by dragging it across the edge of the container. You don’t want to saturate the bristles all the way to the ferrule; dry-brushing doesn’t need much paint.

Drag the brush repeatedly across a paper towel to remove the paint. How do you know when the brush is ready to use?

When the brush is leaving almost no mark on the paper towel, it is ready to use on the model. Basically, the brush is dry, hence dry-brushing.

Here’s where the magic happens. Gently and repeatedly stroke the brush across raised details, like this radio operator’s hatch, to deposit a little of the lighter shade on edges and ridges. Rubbing harder or using a scrubbing motion can add wear or fading to flat surfaces.

Note the effect on the dry-brushed radio operator’s hatch (left) and the untouched driver’s hatch (right). Keeping the effect subtle makes it appear the details are catching light and adds visual interest without making the effect appear cartoony.