Step 1
Draw some random, vaugely floral shapes. There should be no repetition. It has to be precisely random.
Step 2
Start coloring in the shapes.
Step 3
Add contrasting colors. There are rules about this; you can't have two shapes of the same color right next to each other. Except when you have to for some other reason.
Step 4
More colors. Feel free to use earth tones like grey or beige. It doesn't all have to be bright colors. The earth tones help the bright colors stand out without overwhelming the viewer and becoming gaudy or clownish.
Step 5
After filling in all the colors, go back over and outline the shapes with a fine fine pen. This will help the shapes stand out and make the painting more visually appealing. The process becomes a little tedious, but it's worth it for the final result. Extra credit if you use a magnifying glass to make the lines more precise.
Step 6
After you have done all this to make it more precise, go back over the shapes with a water brush. These are watercolors, so they will blend nicely together.