Demesnedenoir
Myth Weaver
Know your ending even if you don’t write it first is good advice, but of course, allow for changes. Of the problems with “high concept” ideas is that the endings sputter and flail. It’ll also give you a destination, and might make finishing easier.
I write my endings first. Then all I have to do is plot it backwards until I hit a boring stretch. That's the beginning. Then I write the middle.