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 each other.

Wet the sky with clean water. Drop in raw sienna and allow to dry. Wet the sky again with clean water drop in cobalt blue - if it runs into the flower shapes dap out with kitchen paper

Dry - mix up blue + yellow + grey  apint 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