Richard P. Feynman who was a physicist gave 4-step technique to learn anything and remember for a longer time. Here are the 4 steps,
1. Select the topic and read the topic you wants to learn.
Reading and Learning is different, just read the topic and understand what you read.
2. Write it on paper and start explaining what you write as if you are teaching someone.
This makes you realise which parts you understand and which parts you have to learn more.
3. Go to references to have a complete picture on the selected topic.
4. REPEAT THE STEP 2 UNTIL YOU EXPLAIN THE COMPLETE TOPIC WITHOUT GAPS.