Painting with watercolor is simply applying a sequence of layers or "glazes" to build value, develop form, and create the illusion of light and depth. My process begins with recognizing the various "lights" in a painting (warm vs cool intense white light). For a painting in which the "light" is mostly a cool, white light (like the Iris below), the white of surface serves as the "light" and I will begin to build subsequent values around that white, beginning with the lightest values. I apply paint "wet-into-wet" for a given area typically using "glazing" pigments for this step. Glazing pigments when diluted with water are transparent, liftable, usually non-staining, and will not appear "heavy" or "muddy" over the course of adding layers. (Below: cobalt blue, viridian, permanent rose, aureolin yellow, and dioxazine violet) The challenge in watercolor...preserve the light and not cover these areas with paint...look first, then paint.
For yellow-warm or combinations of light, my first step in the layering sequence is to paint in the warm "light" with the appropriate yellow (usually Aureolin or Hansa Yellow Light), but still using the surface to reflect the white, intense light. See previous demonstrations.
My method for applying paint to aquabord: Wet-Into-Wet. Wet the surface of the area you want to work. I will often work in "compartments" (i.e. one pedal at a time). Saturate the area until the water stands on top of the surface. Drop in paint toward the edges where you want the most color, leaving the white areas. Drag your brush toward areas that you want value. Drop in more color as needed. Lift and tilt the board to allow the water to mingle the paint until you are happy with where the paint will settle. Let the water do the work. You will see subtle changes in graded value that will begin to describe the form. Once the paint has set on the surface, you can move to an adjacent area. Continue the process until you have covered all areas as needed for this initial step.