But this is rapid rating, not Blitz or bullet, and I only play 45 minutes matches with 45 seconds increment on chess.com (which I think is not actually classical and not rapid, but marked as rapid on chess.com).
I don't do puzzles, study cards or anything, I simply took a couple of opening video courses from Simon Williams on both white and black, and played those exclusively.
Initially I played 15 minutes/10 seconds increment games, several a day, until I felt that I was losing a lot of winning positions only due to time.
Then I increased to 30 minutes, and now 45/45 which is almost a classical format.
I don't think playing short time formats is ideal for learning, I like playing longer ones and really think the games through.
Then analyze each game thoroughly with chess.com post-game analysis.
I only play one game a day, almost every day. Most games end in well less than an hour, but some take close to almost two hours (due to the increment and long end games).
I think like in any game, if you continuously play with opponents of just about your skill level, and you analyze your games to make sure that you are not making the same mistakes again and again, you will improve over time just like with anything.
To minimize rating fluctuations and tilting, playing only one long and well thought out game a day works great and keeps it fun.
I think to keep it fun, it's important not to forget that rating fluctuations are normal and don't mean much. As long as you keep playing and analysing each game, improvement is possible.