Roughly sketch the composition, its a good idea to design your composition so that painting in the dark background will be easy, so draw the petals touching the sides of the paper, then you will have smaller areas of dark to paint

Wet the flower area with clean water. Drop in lemon yellow and burnt sienna and allow to dry.

Dry - mix up blue + yellow + grey  paint roughly around the petal shapes note the background is different colours but is really dark. We want to have some strong lines and some blurred lines - lost and found edges. Lost edges use clean water to blur the petal edges