Salt is a great way to get anomalies and differentiation in field of watercolor. Use a really damp paper with a generous amount of pigment to really bring out the "stars" and celestial like patterns with salt.
STEP 1 - Dampen the paper. This is called wet on wet.
STEP 2 - Apply pigment. This can be in bands, shapes, zig-zags, diagonals, or other form.
STEP 3 - Allow the colors to bleed into one another. You can do this by turning the paper, or just placing it on an uneven or angled surface.
STEP 4 - Apply salt on top of the pigment while the painting is still wet. The salt will absorb and pull the water away from the paper, taking the pigment with it. When the painting dries the salt action will show up as less pigmented areas of lighter value. It will look like a starry or snowy sky. This is great to create celestial, or even winter scenes. It adds a bit of wabi-sabi like nuance.