Fairy Story Started

So since I've got some time at work now, I've got time to do some writing, even though I'm not done with Blood 2 revisions. So now I'm working on my fairy story. Problem is I've got no plot. I feel like I don't have enough information to go on. I wonder what to do in this case. Should I flesh out the world-building more, until I've got something, or just start writing and let the world-building flow more organically.

I think the problem is I've got the opening scene idea, but I just can't see it clearly enough. It's like there are gray parts clouding the picture in my mind. I don't know what those are filled in with. I guess I just can't decide which way to go, like a choose-your-own-adventure book. I don't know which one will yield the results I want.

I can't remember what I did for Avatar, I can't remember how much world-building I did before I started writing. I seem to recall having almost no notes, besides the visual in my head. Then as I went on, I started making notes about what was going to happen next - very short, just for reference, nothing super far in the future. I ended up restructuring the story heavily, and I'm not sure how solid a story I ended up with - the rejection letters are not very informative.