It depends where you are now and where you want to get to? Are you >20 handicap, 10–19 handicap, 5–9 handicap, <5 handicap? What’s your goal?
Practice. But preferably don’t practice a bad swing, take a few lessons from a golf pro then systematically practice what he or she teaches you. Most folks seem to take a lesson and may not practice what they are taught till they turn up for the next lesson. Usually they don’t advance much if any. BTW if you can’t afford lessons watch the free ones on Youtube or the golf channel.
Play more, maybe a lot more. Be realistic, how much you practice and play likely determines your consistency - single handicap players mostly play/practice multiple times a week.
Analyse your game - don’t just keep score, record and analyze everything. Where do your strokes go? Improving which parts of your game would most improve your handicap? Clue: it’s probably 50 yards and in :-). Have a playing partner smartphone video your swing, analyze it with the V1 software (you’ll find it online).
- Read golf books, watch golf videos : Learn the mental side of the game. Both course management (if you’re going to miss, what’s the best miss?) and attitude/concentration (put a bad shot behind you and hit a great recovery) My personal New Year's resolution is just three words, “birdies after bogeys”. For some folks playing for money forces them to concentrate and they play much better with that pressure.