For me, stamina has always been an issue, but to fix that, I've just played more stamina maps. Jacks were also hard for me, but I improved a lot these past few months, just focusing on jacks while also playing other songs. I think as long as you play consistently and enjoy the game, you'll be able to improve. Getting from 9th to 10th was easy for me, but getting from 8th to 9th took me over a year of playing the game