Analyse your lost games and learn from your mistakes.
solve puzzles and analyze your games
By getting good
Get a bunch of chess books, put them in a smoothy blender, add only water. Then drink the knowledge.
Play a lot of chess games, analyse your games, especially your losses and watch GMs and IMs on youtube. When I was a beginner I watched Ben Finegold's lectures and Hikaru Nakamura's speedruns.