From 1200 to 1600: what actually worked for you?

If you have climbed a few hundred rating points, what made the difference?

Things that come up again and again:

• Reviewing every game — especially the losses — before checking the engine
• Tactics every day, even just 15 minutes
• Playing longer games (rapid / classical) instead of only bullet
• Learning a small, solid repertoire instead of memorising long lines
• Basic endgames (opposition, Lucena, Philidor)

What worked for you, and what turned out to be a waste of time? Let's make this the most useful thread in the forum. 💪