I definitely concur with my predecessors as to the "Say Yes" rule, because it gives the players a stronger sense that they are in control of their own game, and adds more drama. I usually start my games with a point of high action, for example in the adventure I'm running next, the PCs are immediately attacked by a bunch of ectoplasmic entities created by a powerful dark wizard. Finally I like to list a bunch of elements I want to use in the arc I'm about to start, and find relationships, then build adventures around those relationships.
Example: For this arc I want to introduce the players (most of whom are new to the Dresden Files) to the world, so I want to include many of the larger elements, both: monsters like the fallen, vampires, and the fae, and conflicts like the war with the reds, and the lack of white council control in our city. So the elements I choose are:
- vampires
- wizards
- fae
- demons
- angels
- knights of the cross
- mob
- outsiders
Then I relate them to each other, and use those to create adventures (at this point I make tentative titles as well)
Perfect StormCold SnapStorm's Eye- Angels
- Demons
- Knights of the Cross
- Outsiders
Finally, I make it into a flow chart, to show how the adventure comes together. So that's how I do things, I hope it helps.