How do I get to 800 elo from 400 elo in chess?


For me it was watching youtube videos that teach the principles of the game. Then playing rapid games to take some time to think about each move.

Improving at chess is usually not easy. If you can afford few lessons, I would advise getting a coach. I can teach you how to think during the chess game. After that, your progress is inevitable.
If you can't afford any lessons, here is the excerpt from very good article on how to improve:
Play a lot, analyze your games, and primarily study tactics. Your knowledge of openings, endgame, middlegame, etc. will come from analyzing your games and going over grandmaster games. Only study one of those specific topics if it is clear you are specifically losing because of that topic.
Source: https://www.gautamnarula.com/how-to-get-good-at-chess-fast/
Good luck either way!
Can some of you suggest some tips?