Just think of any one idea you want to express, and start with it. Forget about structure, punctuation, where it belongs in the piece, and forget about what other points will need to be there to reinforce or put that idea into perspective. (Where you start might not even wind up in the final copy!)

Or,

Start writing about how you've got writer's block.

E.g.,

[Jeez! I've got writer's block, and I can't think of how I'm going to get the idea of how to pack so that getting through security is a breeze. I mean, if folks only knew that . . .]

See?

Hope it helps.

Marye