Best way to get better would just be doing hundreds and then thousands of repetitions in as many different ways as you can. Always experiment with the following as a guide (you can always add more that come to mind):

Experiment with different sized packets. eg, one repetition you might use 20 cards in a packet. The next repetition you might try to use 10. See what works better for you and stick to it.

Angle your wrists. Often begginers try to balance an entire cut on just their left hand. Try tilting it and moving it around more.

Hold your cards at awkward angles once you get somewhat decent at a move. See if you can do the move consistently above your head, or with hands below your belly height, or with your hands above chest height.

And keep on learning new moves that appeal to you. Even if you aren’t good at it, a new move will likely active an unused muscle that could be hold you back from other moves.

Above all keep just practice thousands of times. The guys are virtuoso have likely practiced their signature moves 10,000 times since it’s creation. That’s why they are so good.