1. Decide on the topic
2. Find the expert in that topic from Google
(Expert is someone who has either won some prestigious award in that field or is a pioneer of the field or has several years of experience)
3. Search him on YouTube
4. Find 10 videos which are more than 20 minutes in length and create a playlist.
5. Watch all of the 10 videos and write down the points which are repeated more than 2 times
6. Focus on these points. That's all!