One of the reasons I love working with watercolor is the variety of techniques for creating textures. The above image is a collaborative piece I've been working on with one of my talented friends and artist, Nen. This is after a couple of rough salt texture passes which we're using as a base to build on with watercolor, gouache, and some acrylic.
alt has some interesting properties and through some experimentation I've found different salt types to affect watercolor washes differently. For the above image, a mixture of 3 or 4 salt types was used with a heavy amount of water in the color washes. Once it set, the heavy salt was scraped away and another wash was put down with a lighter salt wash this time. The resulting layered texture will form detail elements for veiny wing membranes, and hard scale textures.
For my spacescapes I also use a base salt texture. See the below WIP:
Another useful tool is a stiff brush or squirt bottle. Spraying pure water on a darkened wash, or a watery oily mixture, even a color can also add a resist effect where droplets fall - great for glows around stars.
Other textures can be easily created without the use of anything but color, water, and brushes. One technique I like to use, is a long thin lining brush and rolling the brush on it's side at an extreme angle to create a flame effect. The long brush fans out with color and contracts as you pull it laying color down organically.
The same technique but with a broader brush can be used for swirling clouds. For larger fluffier clouds it's. eat to start with a wet paper and lightly dab color in areas. The bleeds can be brushed out and blended as you go creating a smoother cloud gradient.