Thanks for all who contributed on this and similar threads. I'm happy to add my experience.
1. Attended in-person 2-day courses Intro to Scrum, Product Owner, Scrum Master from http://www.agilesparks.com/
2. Learned Agile Coaching by running our coaching team using Scrum, and learning for ourselves and when coaching software development teams with regular reference to http://scrumtrainingseries.com/
3. Transformed 10 development teams to Scrum over a year's time
4. Read Ken Rubin's Essential Scrum
5. Read this and similar forum threads
6. Spent maybe 3 hrs/day x 2 days re-reading The Scrum Guide, taking all the Scrum.org open assessments, with multiple runs of the Scrum open assessment until I was at 100% repeatably. I took advice from forum posts to read about burndown charts to make absolutely sure I hadn't missed anything about them. (I hadn't -- they're pretty simple.) Also took testtakeronline's free PSM1 prep test several times -- good for the tricky multiple-selection question format of the real test, and a wider variety of questions. And the http://webgate.ltd.uk/scrum-aide-memoir/
was helpful as a final review.
With that, I passed the PSM1 test on the first try in about 40 minutes with a score of 95%.
Extra notes about taking the test:
Be very aware that as soon as you've answered all questions, the "dangerous" FINISH button becomes active. Make sure NOT to click it by reflex, but rather to leave lots of time to review questions before finishing.
The bookmark feature was useful and sufficient for me. I bookmarked any question where I was not sure of my answer, and went back and reviewed just those. I don't think I changed any of my answers, but it was comforting to review those. I did NOT review questions that I had been sure of first time 'round, because my experience is usually one's first answer is the right one. The bookmark table was also useful for highlighting one question I'd forgotten to answer -- probably double-clicked "next" by mistake earlier. I was able to click the question number, answer it, and continue with my review.
After I had reviewed all bookmarked questions, I looked again at the remaining time, decided I'd done the best I could, and clicked "FINISH".
Result: 95% (means 4 questions wrong out of 80).
The breakdown it gave me showed that my performance matched my actual work experience: I got 100% in the "Scrum Theory and Principles" and "Coaching & Facilitation" categories, which makes sense for my having been an Agile Coach!