I liked this enough to save it almost 5 years ago when Merlin Mann said it on Back To Work #339 (~10 minutes from the end):
On the first page of every notebook, write "The first page is profound." Now you've started writing in it, it's no longer a new notebook, and you're past the "I don't want to start a notebook unless I'm writing something worthwhile" stage. All sorts of other quick reference things you could put on the first page depending on how you use notebooks, e.g. bullet journal rules if you use that.
Possibly also from the same show, things to write in the notebook for every day:
* What am I thinking about? What's on my mind, one sentence
* What am I worried about?
* What one thing do I have to do today?
* What one thing do I want to do today?
* (bonus) What am I grateful for or
what nice thing can I do for someone today?
On the first page of every notebook, write "The first page is profound." Now you've started writing in it, it's no longer a new notebook, and you're past the "I don't want to start a notebook unless I'm writing something worthwhile" stage. All sorts of other quick reference things you could put on the first page depending on how you use notebooks, e.g. bullet journal rules if you use that.
Possibly also from the same show, things to write in the notebook for every day: