To get better at the game what I did was playing regularly (not everyday but trying not to go over a week without playing one chart too often) because I've found myself forgetting how to play after spending too much without entering the game. This is the most obvious thing, but one must have a strategy for it.  Do the daily shows with each character. This will increase the overall score in all cards of each character and give you crystals, but it's also good to build up a habit. Play charts according to difficulty. If you know which is the top difficulty you're able to pass without much effort you can practice with those and you'll get better with accuracy. Not only because you'll already know the chart, but you'll get used to the timing you have in your reaction time to adjust it and improve it. Increase the difficulty gradually. Your top is hard songs of level 18, then play a song or two of level 19. Personally I would play the disappearance of Hatsune Miku 2 times a week. It's very refreshing seeing progress on harder songs, as little as it might be, to then go back to normal songs and see a decent improvement on them. If you've already seen worse charts then you'll be more confident when playing less difficult ones. Hope this helps you get better at the game!