I can try the best I can to help!
It always helps if you have strong characterization. I find it easy if you openly say how a person is in one shots, since you don't have the time/length to show it through actions.
As for format, I find the hardest part the beginning and end, which is why I often mirror songs. But the format should be very simplistic and you want to really pull the reader in since you don't have a prologue/first chapter to do so. It needs to be relatively fast paced with lots of thoughts to help narrate.
Scenery is always important since typically, the one shot only is in one place. But neglected that in Payphone, but her thoughts were the main priority.
I always start off the thought process as very long and exaggerated in the first few paragraphs, and if you noticed in Payphone, the later it progressed in the song, the shorter the paragraphs became. I find it easy because it's always easier to conclude on a smaller basis.
Um... I'll try to think of more stuff, but is there any other specific things you need help with?