I know I personally like to sit down and hammer out some of the background, the rules and the set up of the story along with the names of the key NPCs. I may or may not write down the focal point of the story, the “McGuffin” of the story if you will.
From here, I will just run with the campaign, taking it session by session, always reacting to what the players do with their characters.
Based upon this information, I will jot down a note on a sticky so I remember it or write it in a DM Journal, so I know next session, I want to branch off of this and it worked really well.
What say you?