Well I've been fretting over game-prep for today's session, including posting this thread.  mrlost had some good suggestions, but still wanting to come up with a method rather than simply rely on other peoples' ideas, I finally cooked up something that seems to work well for me.

It works well in-tandem (or zoomed-in detail, perhaps) with the awesome Adventure Funnel thing.  Basically it works like this:

First, come up with the Goal (or even multiple goals).  As Robin Laws says, a goal should be a simple statement, beginning with some sort of action.  It should have a definite conclusion point.

For my session, the goal was defined as: Get through the blockade.

Next, we work on obstacles.  This is the next step in the Adventure Funnel, but my brain needed a little more structure.  In this case, a simple framework:

(noun) (action) (noun), preventing the PCs from (achieving goal)


I found that this got my brain revving up in the right sort of way and finally managed to come up with four or so obstacles that work for me.  Fleshing them out shouldn't be too difficult.  Here's my examples:

1. Sindran patrol ships block the channel.
2. Sindran wizards summon a whirlpool.
3. Sigfried challenges Crispin
   because he has stolen the map.
4. The kraken rips off the Mako's main-mast
   from beneath the waves.

As you can see, the first obstacle is the most obvious one.  The other three are added complications.  In each case, the statement has a phantom appendage of "...preventing the PCs from running the blockade."

In cases 3 and 4, I've added what might be termed "details" in the Adventure Funnel parlance.  These are just things that give the obstacles added context.

I realize that this framework may be highly individualized to my thought process, but I found that it really helped me brainstorm ideas, so figured I'd share it with the board.