Use glue, salt, and watercolor. The glue makes the colors rise from the paper and the salt creates a 'starburst' look.
watercolor + gauze • wet paper, add gauze, cheese cloth, etc., saturate with color, let dry completely and take off
I love how this artist used Winsor and Newton Cotman watercolors to test different texture techniques. (On Arches 140lb cold press, using Winsor Newton's Cotman watercolors, my favorite paper and paints.)
Watercolour Texture Techniques
Beautiful Watercolor Process by Momental Designs via Oh So Beautiful Paper
Water color tutorial by ~i-am-yaser Interesting technique with Bubbles.