My advise would be.
Try to play alot of DT and high BPM maps, focus on reading too. Sometimes is not how fast you hit the keyboard but how effectively you do it. Try and remember, when you started out with the game you would maybe attempt a map alot higher than your skill level and speed, and even though you would try to tap as fast as you could, it seemed like it was too slow. Now think about those maps that you can do now, are you really hitting much faster? well probably yes, but for the most part what made you pass those maps now is the reading ability you acquired. Sometimes is not that you don´t have the speed but you lack the reading for some streams or single circles.
Another advise would be, try to press the keys as lightly as you can and hold the pen as lightly as you can. If you´re not warmed up it may seem difficult, but as you play more try to have a mindset of lightly tapping the keys and holding the pen, and doing it fast. It´ll eventually give more stamina too.
Gl