Laying rails for the locomotive

Some writers are able to think of stuff while they write.

I sure can think of stuff, but it is almost always clever, glittery distractions from whatever it is I am trying to accomplish. Pointless flashbacks, cool devices, elaborately describe artworks...name it, I've done it.

In order to actually write a scene, something unified in space and time that has a structure and focus and conflict and a decent ending that kicks you into the next scene, I have to already know all of those things befor...