Hi!
There is no straight answer, the best way to imporve depends on your current level and skills, available time, personal preferences, resources you get and other factors.
I wrote a post on the subject it might be of interest to you:
https://www.chess.com/blog/maafernan/chess-skills-development
I'm a chess.com coach, you can contact me anytime for customized coaching at an affordable rate.
Good luck!
Hello, I have been sitting at 750 ELO for about three years now and I was wondering what the best way to improve would be because clearly I have not found it.