DT demands:
- high BPM (speed)
- high AR
- high precision
For the BPM you just start playing maps that are slightly faster than you normally play and get used to it. I'm having an issue with this right now, but figured that I do not lack speed but rather consistency on high BPM jumps, so I'm training it right now using practice maps
High AR is rather easy honestly. All you have to do is to constantly play maps gradually increasing AR. There is a very convenient Lazer mod "Difficulty Adjust" where you can literally select any AR for any map, so you can force yourself to play even slower maps with high AR. When your brain will get used to it you'll be able to comfortably read higher AR
For precision just try to tap more precise and get rid of 100/50, look at error meter to check if you're too slow or too fast and adjust accordingly. No special tricks there, just some practice, not the hardest skill to learn
As for alternation I do struggle myself to understand if my technique is good enough and won't slow me down later on, but what I did was literally spamming 2-3* maps making conscious effort to tap with different finger each time until it was automatic. Then I figured I struggle with triples, especially when they start on secondary finger, so I played a lot of triples (practice maps on Half Time (speed adjust)) as well as normal maps with triples and it went away