I started some of the more time-consuming detail--the repeating floral motif on the piece of backdrop fabric--then decided that the background immediately around it should be done first, so that the looser work of the sky and trees doesn't slop over onto the pattern. So I started by establishing the treeline:
...and then started working on the sky. It's loose, thin, and brushy right now, which I didn't originally intend, but which I like well enough that I'm going to leave it as is for now. Same with the choppy blockiness of the trees' silhouettes. Adds a little bit to the ominousness, I think.