One of the many things Lynda Barry has taught me: If you don’t know what to write in your diary, you write the date at the top of the page as neatly and slowly as you can and things will come to you.
“Going through the motions” is often thought of as a bad thing, but it is the artist’s great secret for getting started.
As I wrote in Steal Like an Artist:
If we just start going through the motions, if we strum a guitar, or shuffle sticky notes around a conference table, or start kneading clay, the motion kickstarts our brain into thinking.
Get your pen moving, and something will come out. (It might be trash, but it will be something.)
For a comedic take on this, see: SpongeBob SquarePants.