Usually I have no choice. I forge through the Valley Full of Clouds and blaze my trail on a scene-by-scene basis, the muse not deigning to point out the next tree until I have each one down. Sometimes I can do a higher level one -- heroine goes to the mountains in search of the macguffin to save her father and brother from the tyrannical king; heroine finds another macguffin that tells her a way to defeat the king; heroine goes down the mountains into another kingdom and uses the macguffin there -- but I still have to write the scene by scene one.
Which means I can go merrily along, building scene by scene to the crucial turning point that was one of the first things I conceived of -- and realize that I don't know well enough how it happened. The heroine gets abducted. The kidnappers do not have access to anywhere where she would be outside castle walls, and she would prudently remain inside during an assault. Hmm. . . hmm. . . it would help to move her about the castle, which I probably can do. . . . .
At least I'm not working out these details with the finer ones you need to actually write the scene. That's why I took up outlining in the first place. 0:)