Say what you will about certifications, I quite like the idea of self studying with an aim to gain something. I already hold a couple of Scrum certs and have found the study process to be much more focused when you know you have to prep for an exam, but that’s just me.
So here is what resources I used:
Scrum Guide (Obvs)
This is your single source of information for everything, read it as many times as you can, 8, 9, 10+ times. Your interpretation of it will change every time, the trick is don’t guess, the answer to every question is in there – even if you have to put 2 and 2 together.
This is a really good course to just jump on, give it an hour a day, whatever you can. It focuses on the scrum guide, real world examples and navigates some of the trickier questions that might appear. There is also some excellent practice quizzes too!
Great book (buy locally if possible!) – it’s pretty in depth and it’s a book I know I will return to over and over again.
I still think this is the best Scrum book out there, it’s an oracle of information in a very slim form factor. If you work in Scrum, you should own this regardless.
Do the Scrum Open assessments over and over again, both the PSM and PSPO one. Get 100% in the quickest time possible.
PSPO 1 is not an easy exam, there is some questions on the Evidence Based Management guide too which might move you out of the traditional confines of the Scrum Guide so read that a few times too. With an hour or so a few times a week and some dedication towards this goal I managed to score 95% which I was pretty pleased about.