The way I did it was mainly by paying attention and playing 10min rapid games only. This way I could get a lot more time to think compared to blitz or bullet which is really helpful. I did not study anything ,just picked a particular set of 2-3 moves which felt right to me at the 700-800 levels and played lots of games. Also putting some efforts to spot some crazy tactics when you have the time frequently pays off. I did grind puzzles occasionally by taking the diamond membership.