As with the cling wrap, simply sprinkle the salt onto the wash of color while it is still wet. The salt will pull some of the color to it and pool around at the same time repelling the rest away. For those painters who like landscapes, wax can be an invaluable tool. Wax resists can be done many ways but probably the simplest is to take a colorless candle and rub it onto the paper before any color is added. Many watercolorists find sponges a nessitity.
Sponges are great for lifting color from a wash.
It is great for softening edges as well. Sponges are typically used to absorb excess paint when too much is laid down. A stiff brush, like a toothbrush, can be used to create a speckled effect. However, when doing this process, be sure to do it in an area that will not be harmed by specks of paint everywhere. With this effect, it is difficult to control the splatter.