If you are reading this article, I assume that you've already made yourself familiar with the PSM I (Professional Scrum Master I) exam. So you won't find any basic instruction in the content such as "The exam comprises 80 questions, multiple choices" etc. However, should you still need fundamental information regarding the assessment, please see the the official resource.
To begin with, if you are not planning to register a course for PSM I exam you may need to find proper study resources including sample quizzes, books, articles and forum discussions. Banding those resources together in a single platform to facilitate your self-preparation is the underpinning reason for this post.
Resources to utilize:
1. Official Scrum Guide
Read it five times at least then go over and skim the significant sections. Learn it by heart and try to comprehend the motivation behind the actions suggested in the guide. Actually, I found it helpful to write down all components comprising scrum framework (R.A.R.E.S: Roles, Artifacts, Rules, Events, Scrum Teams), break them down to sub-topics and elaborate their content without checking the guide.
2. Open Assessments
It can be claimed that the open assessments are the most beneficial tools to foster your preparation process. Because, the real exam contains approximately 5-10 questions from these assessments at total. Not only will you save a tremendous amount of time by adjusting yourself to these specific questions but also you will be able to consolidate the knowledge you elicited from the official guide.
There are three open assessments you can utilize:
1. Scrum Open (The most important, try to score 100 % three consecutive times)
2. Product Owner Open (try to score 100 % three consecutive times as well)
3. Nexus Open (There will be 3-5 questions from scaled scrum. Before taking the test, I strongly recommend you skimming Nexus Official Guide)
3. Mikhail Lapshin's Quiz
Honestly, at the beginning I was contemplating to list all mock exams together in a single topic. After careful consideration I decided that Mr. Lapshin's PSM I Quiz is deserving its own title since it covers the most of the knowledge base that should be mastered.
The quiz features exactly same number of questions with the real exam and it has similar difficulty level and scope. Focus on "Learning Mode" which enables an explanation box concerning the correct answer before proceeding to next question. When you finish with the "Learning Mode" you can test your knowledge and time management skills with the "Real Mode". The web site also contains a scaled scrum quiz which I found very useful.
4. Scrum.org Forums
Some of the niche questions and misty situations not clearly defined in the official guide have been answered in Scrum.org forums. You can even find some users searching for answers regarding questions from the real exam. You won't regret visiting the forums and even involving discussions.
5. Further Readings and Other Suggestions
During your preparation, in addition to the resources aforementioned you can reap the benefit of making some good reads related to Product Ownership, Lean and Agile Project Management.
Last but not the least, be wary of potential confusion that might be triggered by being overwhelmed with the resources inconsistent with the official guide and/or not up-to-date. For instance, lately I've been coming across many PSM preparation web sites persistently indicating ideal size of Development Team as "between 3-11" which is not true according to the official guide.
Good luck with your exam.
Should you have further questions regarding the exam and preparation process, please do not hesitate to contact me.