Study and practicing openings. By this I mean you should memorise all the lines of an opening; not just the main lines. A vast majority of matches are won/lost within 30-35 moves by a few botched up opening moves.
I don't recommend puzzles that much. They give you mental satisfaction. However, it is one thing to think of a good move knowing before hand that there's such a move possible but entirely different to recognise that you are in such a situation in the middle of a game.
Studying openings is a waste of time, even counterproductive, if you’re a beginner who hangs pieces all the time. This advice is much better suited to someone hoping to get over the 2k rating milestone. If you’re below 1k or even mid teens then your best bet is just to play a lot (longer time controls against better opponents) and study your games to look for your blunders, mistakes, and inaccuracies.
I tend to agree (& thought similar about puzzles) but I think they are effective at training your pattern recognition so you more easily find tactics when you play.
I don't recommend puzzles that much. They give you mental satisfaction. However, it is one thing to think of a good move knowing before hand that there's such a move possible but entirely different to recognise that you are in such a situation in the middle of a game.