The truth is, the whole painting is based on one simple approach. Here's how it works. First, make the paper wet. Then wait until the surface is no longer glossy, but still damp and cool on touch. Next, apply the paint, varying the amount of pigment on the brush depending on your needs.
On the picture below, this approach is illustrated by the brush strokes in the middle. They are well defined, but a little bit diffused, which creates a nice and soft appearance. The brush strokes on the left were made when water was still sitting on the surface. The ones on the right were applied on completely dry paper.
In other words, all you need is catch the right moment, when the paper is not too wet and not too dry. This maybe not quite as easy as it sounds at first, but it certainly comes with practice.
Happy painting!
