Study the endgame, it servers more than you'd think.
Learning openings is nothing. If you don't master the endgame, than you're just premoving stuff and not playing real chess.
After that, spend 5 second between moves. I had the bad habit of play in 2 seconds, even on daily chess, and didn't serve me well
Do a lot of puzzles for practice. The more puzzles you do the easier and by easier, I mean less hard thinking, do you need to do to identify patterns. Good players don't think less hard than newer players. They just know what they do and don't need to think about. Think of puzzles as just like lifting weights. You want to be able to lift 150 lbs in front of a girl effortlessly, well that will be a piece of cake if you can lift 300 lbs in training.