▲ disclaimer ▲ stop immediately if you feel (sharp) pain. i'm just one of normal tapping players. health is the frist thing you have to take care of. do at your own risk. oh well ofc im not a top player and this can be wrong lol
speed: try singletapping. make the power you press the key strong.
stamina: try mashing in consistent speed. start with ~180bpm long stream if needed. (try fc -> 95% -> 99%)
basically you have to develop the power you press the key and make it consistent. but when you actually play the game, you have to be flexible depending on the situation you face off. you need to change 'tapping mode' between mashing(burst/stream) and power-tapping(fingercontrol) for what pattern requires.