The procedure I usually follow then tackling a new subject isn't a one-shot approach but an iterative process. The process consists of the following steps:
1. survey key topics that represent either basic aspects of the subject of interest that are required to understand it or have important practical uses
2. organize these key topics as a project by breaking them down into individual tasks based on interdependencies and key productivity goals (i.e., I want to be able to do something and add a skill to my technical tool belt)
3. compile a list of reading material that cover the key topics
4. while reading on each topic, write a monograph of sorts on the subject. The monograph is intended to help you track the progress, evaluate what I know and don't know, synthesize what you do know and refresh your memory (particularly useful if it's a medium/long-term project), and help understand where to guide the learning project to better reach milestones and mitigate potential shortcomings.
Step 1 and 2 are updated based on what I've covered in the monograph. The monograph is updated as I progress, and If I didn't added the monograph then it's as if I didn't covered the topic yet.