Make notes after you understand a given topic, not before it. Every aspirant faces such problems in the beginning, so stay committed. I would advise you that before you start preparing a topic from a detailed reference material, say a recommended book, you should try to read/study that topic from a source that just gives you an overview of the topic. YouTube videos can help you a lot in this regard. On the contrary, if you start studying that detailed material directly you may fail to grasp the bigger picture.
So,
1) make an outline of what you are going to study
2) watch a short video related to it if possible.
3) consult notes-type material to understand the topic
4) study the source which covers your topic in depth.
5) Finally, prepare mind-maps, especially for topics that give you a tough time. You can do that on paper (watch a youtube video), or you can download the free version of the Xmind Xen software to create aesthetic mind-maps. I prefer the later approach.
Best of luck