I've taken a lot of courses over the years in udemy.com, but still after doing the course, I forget what I studied pretty soon. So I started experimenting what works for me and I think I found the right approach. I use this techniques pretty much what I do. Whether it is a Youtube video or studying any book, I started taking handwritten notes and review it occasionally. Though this is long process, few extra hours will help you retain the knowledge into your long term memory. And use the knowledge when it's actually required.
Resources mentioned in the video:
1) AWS Training:
https://learn.cantrill.io/p/aws-certi...
2) Practice Exams
https://portal.tutorialsdojo.com/cour...
3) Course Duration Helper Site
https://cantrill.io.i-aws.cloud/